I bought my Commander used with 29K miles on it and it runs great. I was wondering, even though I am taking very good care of it, if the previous owner stayed up on the maintenance. Is there a way to tell if I have any any sludge, or is there an aditive to put in to clean it out good just to be sure? OR, sholuld I just follow the "if it ain't broke, don't fix it", saying? What about you guys that bought yours used and don't know how well it was maintained? Does engine oil itself atually do and "cleaning"?