If engine oil is getting over into your primary, it is probably coming in thru the crankshaft bearing seal. I don't think there is a check valve from the engine to the primary cover. you may need to replace the crankshaft seal.
re:Bart...XLH is a sportster, and was never built with a panhead motor. Also, a leaking valve would not cause engine oil to get into the primary case. stick to what you know, you will look a little less like a fool.
