Most stovebolt distributors have a "reverse helix" ground into the shaft that's supposed to move oil toward the bottom of the housing. Try dismantling the distributor and cleaning that groove out, or maybe even deepening it with a ball-shaped carbide cutter in a Dremel tool. Also, be sure the road draft tube isn't clogged and letting pressure build up in the crankcase.
Jerry
Jerry - What's the best way to check the tube? and clean?
