My 1999 GEM leaked from the input shaft. I replaced the bearing 3 times but it still weeped.
There is enough room to press a sleeve on the shaft (sealed with epoxy) and use a regular seal.
Specs. .960 OD .250 length ID .005 press fit.
Seal 47mm OD 25mm ID 6mm Thick
This is the way current units are built.
Don’t forget to remove the bearing seals.