i think your real problem is much more serious, yes there is a gasket between the trans & transfer case. but that cavity isnt supposed to have fluid in it, there is even a notch at the very bottom for any fluid thats there to drain out. you most likely have a bad output shaft seal on the trans. if the trans level was good but fluid was leaking from this spot, you could have a bad input shaft seal on the transfer case. when i changed out my transmission a few years back, my most difficult problem was getting the T-case to un-dock from the trans. one of the steel alignment dowls was corroded to the case and it didnt want to seperate. check your shift-rail plugs and trans output shaft seal while you have it apart. you should see that drainage notch im talking about when you have things apart also. it will be easier to pull both driveshafts out of the way. while a little awkward, the T-case isnt too heavy, i had my truck up on ramps with the front end and the rear frame supported with blocks so the truck was level. it will help some to drain the oil from the T-case, it doesnt hold alot, but thats weight you wont have to deal with while your wrestleing with it. i beleive i had the mtor supported with blocks at the oil pan and transmission, pulled the crossmember, you'll either have a wireing harness or linkage for the transfercase to unhook and the speedo cable from the rear of the T-case. once you get it all back together dont forget to refill what youve drained. i wish there was a way to fill that extention cavity with fluid. then it wouldnt matter at all if you had a failed trans output shaft seal or a failed T-case input shaft seal. both the trans and T-case take the same fluid anyhow. good luck with your project, and let us know how it goes.