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.