I don't have the part #'s handy at the moment, but when I rebuilt my 51 box a couple of years ago, the seal and bushing was still available from GM. I just went to the parts counter at my local Chev. dealer and ordered them. Had them the next day. From what I read at the time, the GM seal was better quality than the aftermarket one available from the vendors. Several people had trouble with them leaking.
Bob
