Transfer case. I hear a slight whine from the transmission and upon inspection the rear transfer case has a leak. Is this a priority fix?

check and inspect rear axle -----transfer case

If it is a four wheel drive check your tail shaft or drive line by securing the vehicles front wheels jack up the rear tires and in park try to rotate the drive line if you can hear the transmission sound like it is going into gear the transfer case could be damaged! If not a four wheel drive pull the transmission dipstick and look to see if the fluid is dark red or metallic grayish color if so then you're clutch disks inside the tyranny have been worn out and it needs to be rebuilt!

That's a lot of miles on that transmission! The short answer is "no". Replacing the seal will stop the fluid leak, which should be done. However, the whine is an internal mechanical problem, quite possibly from the rear output carrier which commonly needs replacement. "Struggling going from 1-2nd gear" is not very descriptive. If it's a "long" shift requiring higher speed and rpm than normal then you could be having governor pressure sensor or switch problems, valve body issues or internal hydrolic issues. This one is not likely to be a DIY project. Also, don't waste your money on a "pour-in" additive - it won't fix anything. Find a reputable transmission shop and be sure to ask what the "worse case scenario cost" will be because that's what it will likely cost you. (Speaking from experience in trans shop)

There should be a dip stick near the rear of the engine compartment with a red handle on it for the transmission. You want to check the trans fluid with engine idling and the trasmission in park. If it's full of fluid and the vehicle won't move you are most likely looking at rebuilding the trans. To change the fluid you have to drop the pan off the tranmission and the filter is inside. The filter just pull out, the new filter will come with a new seal that presses into the the pump housing. DO NOT attempt to change that seal, leave the old one in place, unless it is damaged. Unless you you have the proper tools to replace that seal you will most likely damage the transmission housing trying to remove the old one. Also, if the transmission is low on fluid, where did it go? Is it leaking on the ground? You may want to check the transfer case oil if it's way overfull the seal between the transmission and transfer case is bad and the trany fluid is leaking into the transfer case. You may want to change the transfer case oil too, they both take Dexron III fluid. Good luck!

...I agree with the last poster. My truck had a pinion seal leak and let all of the lube out and it whined just like you say yours did.

You rear planetary set is worn from a restricted cooler.

As I said, trans fluid keeps the internal components "alive"... Low fluid level can cause burning of internal clutches, premature hardening of seals (essential to proper transmission of fluid pressure) as well as lubrication of necessary gear components such as planetary gear set (which can cause whine etc. which you now have) All of these components rely upon a constant flow of fluid for both cooling and lubrication. Depending upon how low and how long these parts had interrupted fluid flow, directly influences how much damage was done. I take no joy in telling you that you may have damaged your unit, I'd be far happier if I could give you a quick, inexpensive fix. But based upon what you have said, If I was working hands-on with this problem, I would make the recommendation I've already made. There are pressure tests etc that can be done at a transmission shop to verify to some degree of certainty what is going on within your unit. Hopefully they may find something other than what I've said. At this point though, it is wise to have it checked out by a professional, before you become stranded at a time when you can least afford to be.

yes low speed whine noise from the center of he vehicle is completely normal every one with the same drive train as your does it. as for jestan flushing the oil will not correct any problems that already exist but it is a good idea to prevent problems from happening

have the rear wheel bearings checked they had a recall on them they get water inside and rust up and whine please rate and good luck -jeff