Was the surface where the cork rides really smooth? Did you soak the cork seal in motor oil before installing it? If the answer to either of these is no, then it is going to leak.

If the cover was fairly smooth, the seal will seat in after running awhile, and stop leaking. Same with one that wasn't pre-soaked. Run it, and the oil will eventually soak into the cork and stop the leak.

I've had tractors that haven't run i awhile leak at the cork seal, but stop once things got lubricated up. I'd run it for a few hours before I'd tear back into it

I have heard of guys machining out the cover where the felt seal goes so that lip seal will fit in there, and then getting a seal that fits the surface on the pulley and the hole in the cover. All you have to do is grind out the 'tabs' inside the cover with a dremel tool. I've never done this one, so I don't know what size of seal to tell you to get.