1995 Explorer Transfer case fliud migrating into transmission

[Tom M Clark]

About 3 1/2 years ago I took my 1995 Explorer to a transmission shop account of tranny slipping. They did a complete rebuild. Has a 3 year warranty, after 2 years 11 months tranny started slipping again. I had only driven 10,000 miles. They rebuilt again. Then speedometer went bad so I paid them to replaced the internal speedo gear in the transfer case. The transfer case now howls when driving so I checked the fluid level, it was empty so I added 2.5 pints. The transmission was way over filled so I pulled almost 2 qts of fluid out. I'm guessing the fluid is migrating from the transfer case to the transmission. Did they put the seal in backwards between the tranny and transfer case? I have heard of the opposite problem of migrating from the tranny to transfer case but not transfer case to tranny. I would appreciate some information before I call the transmission shop. Thanks!