In the middle of a DIY valve cover gasket replacement, lifted off my cover and on the inside(top of cover itself) was a pretty alarming amount of crud build up but only in certain spots. Not the reddish build up that is stuck to your oil filler cap from vapor and chemicals, but a gritty black grime like you would find built up under a leaky engine. The inside looks clean as a church. Cams, chains etc all look clean. Its just on the cover. My question is...Should I wash this off and with what?