[ParisTNDude]

I just did a head gasket replacement on my 84 Corvette with 94,000 miles on it and I can tell you the tops or valve stem side of the intake valves had quite an oil buildup. I can't imagine that condition would aid in the flow of air to the cylinder. I don't think that gunk can come from the gasoline, but I don't know. As for manufacturers recommendations, they still insist you change your oil every 3K miles which most would agree is a waste of money, especially in the modern engines of late. I have a catch can on my car, but haven't drained it yet...gonna do that this next week and it will be interesting to see.