Basically, after about 10+ hours on the oil, 455 w/ a stock pan the oil was pretty abused. I have since installed a 9 qt pan and while going through my preseason check, the plugs had a little carbon along with the exhaust ports on the heads. Someone earlier mentioned that a clogged air filter would load up the gas into the oil causing the darkening. The air filter was pretty much shot and I'm wondering if I should look elsewhere for a problem?