I inspected the dipstick tube connection on the tranny and it was solid with no leaks. I returned my car to the shop where they said only one transmission line needed tightening. They said they ran it for 20 minutes and no leaks appeared.
Of course there was still ATF on my floor the next day. I can't say whether it was left over from the case, but it seemed too much. The last time I saw this much ATF my father was returning the '58 Biscayne to the dealer for Powerglide service.
I suppose I'll give it a week or two to see if it stops. Definitely on the driver's side.