Not to scare you, but my wife's Toyota did that when she cracked the head. The anitfreeze mixed with the oil, causing a whitish/yellowish sludge on the oil cap. But since your's has sat for a while, it could be condensation I guess. Yo might want to try a compression test to rule out a Headgasket / head issue, though. Good luck,
Scott


Scott Mabe I WILL be Phil. 1999 Contour SVT, Tropic Green BAT kit, K&N RU-3530+MAF, Magnecore 8.5mm, some audio goodies, Hightowers, Knauberized, tatoo by Parkedcar.