Left rear wheel wanting to lock when turning real sharp, it is a 2005 ford explorer 4 wheel drive

SOURCE: Rear Axle Bearing

i know for a fact that the bearing comes with the hub., and if the old bearing is badly damage you may need to heat it to remove it from the axel...so this may be a rather big job if your not equipt
with torch or other ...

SOURCE: Ford explorer stuck in low 4wheel drive

put it back into 2 wheel drive, then reverse 10 or 15 feet, this should unlock the hubs.

SOURCE: Left rear axle seal is leaking differental oil.

ok then here is the procedure  1 take off the axle nut
2 on the lower control arm you will find a large nut and bolt i belive the nut is a 21mm and the bolt side is an 18mm. this bolt is the one at the knuckle near the brakes. remove it
3 you will need to pull the knuckle out of the way or a helper to pull the knuckle out of the way so you can slip the axle out of the knuckle.( its a tight fit but there is room to slip it out.)
4 use a pry bar to pop the axle free of the diff. hosing its held in by a spring clip make sure the clip comes out with the axle if it gets stuck inside you will have to fish it out.
5 use a pry bar or screwdriver to pry seal out of housing then use a flat object that contacts the entire rim of the new seal so it can evenly be installed with out getting smashed and tap it in with a hammer. ( a good trick here is to use some grease and pack it into the new seal where the spring is this will prevent the spring from being shocked out of the seal during instalation . the spring keeps tension on the rubber in the seal so it stays tight to the shaft it is sealing.)
6 then revers the above steps. also make sure you are using the right gear lube it will most likely be 75w-140 but make sure you check your owners manual will tell you if it doesnt say on the diff cover. you can cause a lot of damage if you put in the wrong thing. and make sure  you feel the axle spring clip snap into place.
as a note there are two types of axle seals that are used on these so if the new seal looks different than the old seal then the folliowing will be important to you.the seals on these have been redesigned so if you axle has what looks like a cup or dust cover pressed onto the shaft where it goes into the diff the new style does not use this and it will prevent the axle form going in all the way so the spring clip will not lock in and you will have a leak. so you will have to remove it and install the axle without it.

SOURCE: How to remove disc brake rotor on a 1992 Ford Explorer 4-wheel drive

It should just pull off once you have taken the caliper off. It may be seized in place, if thats the case try spraying the back of it with some sort of penetrating oil, let it sit for a bit. THen put some heat on it if you have torches, or beat it with a hammer. Sounds kind of crude...but it works

SOURCE: Automatic 4 wheel drive on Ford Expedition

sounds like its stuck.this was never a good system. if you have the owners manual follow it to a T. ussually if you find a dirt lot engage the 4x4 run it for a few then shut it off. then back up ten to twenty feet this will set things right