Twice now when Ive gone to check my oil I have found a sludge build up on the inside of the cap, its a yellowy sulphurish looking slag, similar to what you get in your radiator when oil is getting into your coolent, (obviously not happening in my aircooled engine). This last time there seemed to be 3 or 4 little globs of water about the size of a match head amongst the sludge. Im not loosing any compression have no change in my fuel economy and when i drained the oil (both times as soon as I saw it) there was no sign of water or any contaminate at all in the oil or the strainer. I change my oil every 5000km's without fail and replace the filter and clean the strainer every 10,000k's. Is it possible that its just condensation building up in the filler tube as the temperature up here varies from 1-20 degrees at this time of yr. or should i be worrying that somehow im getting fuel (the only other thing i could think that would cause this) blowing past the rings even though im not losing compression, or is there some other way fuel could contaminate the oil, The tappets are due to be tightened but not at all sounding like that its a vavle problem.