Output shaft bearing leaks on Briggs/Stratton 12hp?

Is it worth taking this engine out of the tractor and installing a new bearing/seal on the output shaft? Are there any special tools needed? Where do I find the replacement bearing/seal? The engine is a Briggs/Stratton
Model 283707, Type 0140, Code 9501104B: and the tractor has a service tag # 237590. Any help would be appreciated. This is tractor owned by a friend of mine with no experience in removing/replacing parts. I will help him if the part is available.

Thank You

Jeff Green
October 2009