Lance, I agree with the conclusion that short drives (which don't allow the engine to reach full operating temperature) cause the condition with the oil cap. Along with an oil change, definitely clean the sludge from the oil cap and the oil fill port. In the future the owner should make an effort to have the engine reach full operating temperature every time he drives the vehicle, even if it means driving an extra distance to accomplish that. I would recommend using Mobil 1 0W40 oil. Walmart sells 5 quart containers for around $24, plus they will recycle your used oil if you are a DIY'er.

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Fred Hoelzle