Pull the breather cap and see if it blows oil out of it when revving it under a load, like a full pass I have taped a shop rag folded up over the oil filler holes to see if te motor was blowing oil do to crankcase pressure BTW, some breather caps have very little holes in the bottom to let the crankcase pressure out, I switched my stroker motor over to a set of Mr Gasket breather caps and that cured my oil dipstick from blowing out after several runs with the other breather caps