Take a look at this link:
I have a poor seat on an older (1980's) American Standard 2-handle shower and need to find the replacement cartridge. I'm attaching pictures but there are no visible numbers on this type. It would be good if I could just replace the cartridges and the handles.
Thanks in advance for your help!
As you can see, the seat on this cartridge is worn.
Its an american standard aquaseal. I recommend replacing the whole stem but you can get the black gasket as well. Home depot should stock the stem.
I think it is a "Cadet", not an "Aqua Seal" - the washer is smaller. You should also change the seat. The OEM# for the stem is 44261-07. The seat is 13274-04 and the size is 7/16" X 24 thread and it is 1 3/16" tall.