K1500 700R4 rear trans seal
 

I've had my '89 K1500 on non-op for a few years since it got side-swiped while parked on the street. The damage wasn't too obvious at first until I noticed I kept losing trans fluid from the driveshaft area. Let me be clear that this leak is from the driveshaft after the transfer case and not before the transfer case.
I happened to view a TikTok video from Dave/ Dave's Auto Center and he talked about this same problem with a Ford truck.
When my truck was hit the left leaf spring was bent/ unsprung knocked the diff about 1" off. This caused some kind of damage on the driveshaft or output shaft of the trans. There is some kind of seal on the output shaft of the trans that is leaking into the transfer case where it then leaks out of the driveshaft seal.
I haven't been able to work on the truck due to weather and other time and financial factors. The time is coming due where I may have that chance and I need to do a bit of research now. Is the rear trans seal on a K-type 700R4 similar to the rear trans seal on a 2wd C-truck? I want to add that I'm talking about a seal on the end of the output shaft inside the output housing or transfer case support.

Re: K1500 700R4 rear trans seal
 

There is a seal in the front of the transfer case and it is a double lipped seal that seals fluid from moving in either direction. These seals can be very hard and brittle which seems unusual sense there is fluid on both sides of the seal. Usually they have several cracks in the seal material.

With a truck that old the T-case output seal could be hard too. Do to the truck having been hit the T-case output shaft may be bent.

Re: K1500 700R4 rear trans seal
 

I rebuilt the drivetrain in the 2011-2012 time frame. I freshened up the seals and bearings at the time. I wouldn't expect the seals to be brittle. It didn't seem to me like trans fluid should get past the output shaft (of the trans) in the support area of the transfer case. I don't have a good area to work on it now. It's a dirt lot and I may have to create some kind of cement or brick pad for my work on it.