I'm getting ready to replace the valve stem seals on my 75 k5 350 cid and wanted to bounce my diagnosis off the forum here. Some of the plugs get oil fouled within a few hundred to a few thousand miles of new plugs being put in. No exhaust smoke during drive, deceleration, or on start up. I figure I am getting oil leakdown through the valve guides, not past my piston rings. 150,000 miles on engine, no knocks or anything. oil pressure fine. not tons of power, but certainly not as whipped as i would expect it to be. just hoping to squeeze another 10-20 thousand moderately trouble free miles out of it so i can buy some higher priority things before i save for a rebuild.