I unintentionally fell off my change schedule for my 1MZFE Toyota 6 cyl engine on the last fill. I had been doing a 5000 cycle with M1 10-30, then bumped it up to 6000 for the previous change. I lost track of time, and when I woke up and looked at the numbers I found I had put 7500 miles on the oil. Changed it out right away on a warmish Sunday. To my surprise, there was a black layer deposited evenly under the filler cap. It was hard and dry, and gritty when scratched off with a fingernail. It looked to be about a mm or more thick. This area was clean as can be privious to this change. The engine has about 32000 miles on it. My mechanic was not too excited about this. He doubted I hurt the engine and didn't see a reason to pop the cover or worry about it. Just go back to the regular pattern. I guess that's probably true, but I hate the see that gunk in there. My '93 sentra has 188K on it and I'm planning to do the same with the toyota. Any thoughts?