Making sure the flame trap is clean is good but also make sure the small vac hose to the intake manifold is not leaking and the small brass fitting at the manifold is not clogged. Do the oil cap vacuum jiggle test. I prefer the palm over the filler cap test, cold engine.

If you still have an oil leak at the cap, you can slightly bend the tabs on the cap to seal a little tighter. Do this only after you confirm you have proper crankcase ventilation and suction via the intake manifold.

http://www.brickboard.com/FAQ/700-900/EngineSealsBeltsVent.htm#Flame_Trap_Crankcase_Ventilation_Questions