it does sound like a wet clutch system
that starter most likely is a wet starter which means its not only sealed on the bell housing with a gasket, the output shaft on the armature is also sealed.

I would go back and double check that and make sure its not leaking from behind the mount plate around the starter body itself.

If no oil is present around the body of the starter dripping off it then you just need to replace the mount gasket. If you do have oil coming from the starter body then remove it and take it to your local starter rebuild shop and have it rebuilt.