How do I put oil in my stand mixer, what kind of oil do I use

The only place that could ever needs oil is the back motor bearing, and unless you are very mechanically inclined it is a major job. You need to remove all of the electrical components and the motor armature to get to this bearing.
It sounds like you may have a bad bearing. It is possible it just needs grease, but here again, this is a job for a mechanically inclined person. This involves removing the mixer head from the base and removing the lower section of the motor housing. If you do decide to do this make sure you have a new gasket and FOOD GRADE grease. These can be purchased on ebay.
I have rebuilt 10 of this style mixer. If you decide to attempt this yourself, let me know and I will give you my contact info. I will try to walk you through it. and I have one similar to yours that I have taken apart so I could send you pictures.

if its under warranty take it back but sounds like the seal has been broken youll need to get a new mixer

bad sign seal and probably bearings time to go shopping can be repaired but time consuming.

I needed to replace the nylon worm drive in my mixer. When I put it back together, I found that my mixer made a kind of grinding noise. The noise was due to a vibration associated with the cover for the electrical wiring in the back of the mixer. I solved my noise simply by loosening the screw to this cover. The cover is located on the back of the mixer, and the screw is on the top.
Separately, to find instructions for opening your mixer, you can go to http://neilcrockett.com/mixer.htm.

I am assuming that when you oiled it you merely squirted oil in various places without actually taking the mixer apart. You probably did a good thing if....if....it corrects the grinding noise...but...oil is not only an excellent lubricant it is also a very good insulator and if you got oil into the switch area where it turns on then you may have got oil inside and it can be insulating the place where electrical contact is made. For a possible quickie solution you might try to use something to eliminate the oil that may have got into the switch. Best thing is probably to go to Radio Shack and buy their contact cleaner spray can and use it on the switch. That stuff is real expensive though. A cheaper solution might be to use isopropol alcohol if you have some handy or even spray carburetor cleaner as both of them will completely dry quickly. Be sure to unplug the unit before doing this and allow it to completely dry before plugging back in. You can do all of this without taking anything apart. If it then runs ok then I suspect the grinding noise is still there as the gears inside probably need a little grease. If you want to go that trouble you can remove screws and open the case up...carefully...and put a dab of auto wheel bearing grease on your finger and rub it into the area where the gear teeth are. Do not use a big gob of it ... just a little amount is all needed. If you do not have any grease handy you can use vasline if you have some in the house. If the mixer did not turn on after the above dousing of alcohol etc. from the outside then you may need to do the cleaning directly on it from inside...so if you do take the mixer apart spray the cleaner directly inside the switch. When you take the mixer apart do not remove the shaft/motor/armature or other parts...remove only the cover and enough to do the repair. The possible problem is that if you take it apart too much it will be difficult to get back together particularly if you remove the armature and contact area of the commutator where the carbon brushes are. While inside there though look at the copper commutator area where the tiny carbon brushes make electrical contact. They may be pitted or not allowing the brushes to make good connection. To correct this you can spray contact cleaner directly onto the contact area to clean it. Let it dry and reassemble and the mixer should run ok. If the mixer is very old and been used a lot then the contact area of the commutator may be worn so badly that it does not make good contact with the brushes or the brushes may be worn down so much that they no longer make good contact. In that case you would need to actually remove the armature assembly...what I told you not to do above if you are not too good at reassembling things. Once the armature is removed it is easy to take some fine grit sandpaper and clean the copper commutator making it clean and bright copper color like new again. Also if the carbon brushes are almost totally worn down you probably can find some new ones that will fit ok by taking the old ones to your local hardware store as many of them stock carbon brushes nowadays. If you do all this and are able to reassemble the mixer then it should be just about as good as new again. Hopefully you do not need to go to all the trouble of the major disassembly though. Good luck.

Leaking of oil in a stand mixer is not necessarily indicative of a large problem.

Kitchenaid stand mixers are overpacked with oil to last the lifetime of the motor. If the motor sits idle for some time (is not used), the oil may begin to drip from the gears and settle. Oil leakage may primarily be seen from around the beater shaft or planetary action.

A stand mixer can lose up to a 1/4 cup of oil before it needs to be serviced.

It is recommended to run the mixer on speed 10 for 2 minutes in order to redistribute oil back into the motor. In order to prevent future occurences, this is recommended to be done every 3 weeks if mixer is not being used.

You can put in a all purpose grease. I use MOBIL 1 Synthetic Grease (RED IN COLOR) and it works fine -- you will need 3 tubs of 16oz's each tub. The cost is 30.00 or so. Make sure to get all of the old grease out and pack around each of the trans and worm shafts with the grease, then pack around the MOTOR GEAR and then put all back together. While running it make sure you can see the grease and hear the noise of the mixer through the 2 caps that are FILL caps on the head of the mixer. ALSO, you will find that you will lose 1st gear IF you have tigtened down too much on the LOCK nut, SOOOO loosen in small increments until all 3 gears are perfect and strong. ALSO, the key to noise adjustment is to Tighten (WHILE MIXER IS RUNNING) slowly the large nut that controls pressure on the worm transmission. The general rule with tigtening this nut is to tighten it till it will not tighten and then back off the nut -- IF the unit when starting does not run or it seems bound up when you first turn it back on, THEN you have tightened it TOO MUCH, SOOO back it off again (loosen it) until it starts smoothly and when you turn the mixer OFF it should come to a slow stop and not abruptly stop the mixer. Hope this helps some of you out there trying to do your own adjustments --

You can use a heavy weight gear oil or call the local hobart branch for it.To remove oil----Look under the mixer where the beater shaft is in the back and you will see a three quarter inch nut,remove this nut and drain the oil then put nut back in.To fill the unit remove the top cover screws and remove the top,you will see a long hexagon nut in length,remove this and grab a funnel then add the oil---be patient it takes time to fill as the oil is heavy.

The repair manual says that the mixer can make this grinding sound at slow speed, like stir or 2. This is normal, especially until it warms up. This is the sound of the gears turning at slow speed.

common problem. Worm gear & bracket #PS734273 about $36.