Hello Jgl,
I feel for you! Just went through the same issue with a 74.
Lot's of good ideas in the following thread:
http://www.peachparts.com/shopforum/showthread.php?t=185565
In my case, I think it was caused by topping off the oil, it seems to be taken care of by leaving the level down 1/2 quart. But your situation may be different.
Good luck!
Dan