I pulled the tcase and transmission adapter like afreakydad suggested (since I had already installed the adapter), tapped the extension out a hair, and replaced the seal itself with a Timken Transmission seal part# 710058 from AutoZone.
After running the engine for a moment and then engaging the transmission in reverse with the tcase in 2HI (no shafts attached) I had no leaks.
I know the ATF is low, so I'm hoping that isn't what's preventing it from leaking.
I took everyone's advice and ordered the deep transmission pan and Lube Locker which should be in Thursday. I'll swap pans, add more ATF and hope it's a fix.
Thanks for the heads up on the 241 tone ring, Jerry. I'm hoping I don't have to pull the tcase apart, but I'll watch for it.
I'll keep the thread updated. Thanks everyone.
Also found that the Airtex 1S4219 didn't work on my 241. I ordered a Napa Transfer Case Select Switch, part # NOE6002939 since people said they had good luck with it.