Gary --

Chuck's absolutely right on -- go after the flame trap. You can buy the flame arrester insert (a round gizmo about 1" diameter by 1/2" thick, formerly brass, now plastic) or a kit that has all new parts. The full kit shouldn't be over $20.

But be aware that it still won't work right unless all the vacuum lines and fittings, including those mounted in the intake manifold, are free and clean, as well as the "breather box" (mounted on the side of the engine block under the flame trap). The small line from the flame trap to the intake manifold is often plugged solid and must be replaced.

I once had the rear main seal pushed out of its housing from too much crankcase pressure -- a lotta unnecessary work.