I have a 63 Buick Riviera with a Superturbine 400 transmission built in 1964. The trans was swapped by the previous owner. Under normal driving the trans does not seem to leak but if left parked for several days or longer I sometimes find a puddle of fluid on the garage floor. I can't see and any obvious drip points and it does not happen all the time only periodically. I just spoke to another Riviera owner and he has the same issue with his car. Does anyone have an idea of why this happens.
When you shut the engine down, ATF drains from the converter into the pan raising the level. I would clean the case and look hard at the dipstick tube seal.
Or check to see if you have a weep hole in the middle of the driveshaft yoke. I had a weep hole yoke in my 400 and it would dump a quart of fluid after sitting a couple days. Another source besides the dipstick is the front seal. Very common. Unfortunately, the trans will need to come down for that repair. You can put a piece of white poster board under the car to see where its coming from. That may give you an idea what area its coming from- front or back
