Good advice so far.

I will add this. There are two types of seals. I like the balloon seal but often flat seal is all you can get. Both work fine but I like the balloon to keep the dust/dirt away from the sealing surface.

Most balloon seals have small drain hole I put to the bottom so water won't build up in the seal.

Since the transmission shaft sticks out of the middle of the seal I use this ultra high tech seal installer. I know it looks like a galvanized pipe cap but the one I sell is only $12,000.00 and can be used underwater if he need exists.

Seriously the pipe cap works great on most seals and fits like a glove around the balloon.