From the looks of the T case (oily) id suspect you have the infamous "transfer case rub" The oil pump retainer eventually rubs a small hole in the case and the oil weeps out. id definitely relace the Trans output seal and the T case seals when you find one. If the oil in fact leaked out as it sounds I say the T case internals are done for. If you find another case I recommend installing a updated oil pump retainer kit for lack of a better and have the confidence it wont grenade again.

PPE Diesel GM Pump Rub Kit Install

Follow along as we install a pump rub kit from PPE Diesel in the transfer case of our 2020 Chevrolet Silverado 2500HD!

www.motortrend.com

 

^^^^^This.
The NP246 transfer case is super common. So is the oil pump knocking a hole in the case. Even if you get e good used one, put the oil pump Barney in it. It’s not hard to do with the case out.

 

I put the Merchant Automotive one in mine. Definitely a simple job on the bench.

Here is where it wears through, especially if the little clip breaks off that is supposed to stop the wear. Mine was already working through the case, but no hole yet.

 

I would suggest just getting the cheaper pressed metal plate that fits over the original oil pump housing, works just as well as the more expensive billet housing, and nobody can see it, so you can even tell people it has the billet pump...
If the TC locked up, I would be hitting up a junkyard for another one, install a pump rub fix on it, and perhaps also do bearings and seals, and then throw it in the truck. Or get 2, one to throw in the truck right away to make it driveable, and a second to do pump rub/bearings/seals, and then swap that it and sell the first...

 

Finally got around to working on it again, today my dad and I got a junk yard transfer case for $180 and another $60 for new seals all around. Unfortunately the Chevy dealer doesn't have the oil brace clip, so I have to wait until next week for that part. Anyway we put the transfer case in and I'll deal with that other part later. Can I install it with out pulling the transfer case? Also I noticed that there was an obvious slow leak coming from the transmission, but I didn't see a seal to replace. Anyone know what to do about that?

 

If you installed something like that pressed metal plate I suggested as a pump rub fix, then that small clip won't be necessary (it's gm's just barely sufficient if everything goes right idea of a pump rub fix). If you haven't installed a pump rub fix, then I would suggest getting a better one than that clip. You can't install them w/o pulling the TC. And hopefully you looked at the case on the inside to see if/how much it's rubbed through and if it has any pump rub fix installed.

I know for a 4l80e, there is a transmission output shaft seal, wouldn't surprise me if the 4l60e also has one.

 

Well crap, I think I bought the wrong part, I bought a little clip off of Amazon (see picture), and I don't have the time to wait for the rub plate and repull the transfer case. So plan for now is to get the truck up and running and do a full inspection and rebuild later this summer.

 

You can install it, and it does work. But, for at least some people, it has come off and/or failed, and then the pump has worn a hole in the case. It's a poor solution to the problem, enough to get trucks out of the warranty period, and will generally last, but it's not a great fix IMHO.