Depends on where it's leaking, there are a number of places that it can leak. Some of them can be done with the transfer case in place, others can not. There are 2 side covers, neither one uses a cut gasket, both use FIPG (form in place gasket). One cover can be removed easily (the big rectangular one), the other one (on the output housing forward) can't without separating the trans and transfer. I just resealed mine 2 weeks ago. I had to remove the transfer because the forward cover was leaking (as well as the intermediate shaft "o" rings) so I just replaced everything (gasket/seal wise). Best bet is to clean everything carefully, then put oil in it. Don't drive it at first, just let it sit and see if you can detect the start of a leak. If nothing then drive it around the block and check it. You don't want to drive it too much because then the oil gets thrown around and it's hard to determine where it started. If you haven't downloaded the RAVE workshop manual, I'd suggest it. The links are on the signature lines of a couple of members. HTH

 

Ok sounds great and yea I down loaded the manual. Nice to have that as a reference!
Have you done the rear differential? that is leaking as well. Oh well it is a 99 and I'm looking forward to restoring it to hopefully near new condition.
Cheers!

 

I haven't replaced the rear diff pinion seal on mine (it's not leaking), but it's a pretty straightforward job.