I had an oily substance spot on my corvette top when I bought it. Tried a lot of things, but finally I used "Dawn" dish detergent and that got most of it, however, still could see the spot in certain light. A friend told me to use lighter fluid on it; now that made me extremely nervous doing it on a corvette; but since nothing else worked I tried it, and it did indeed work! Mine is a canvas top, if yours is vinyl, most cleaners should work.
Just another reason to not use hydraulic sytems where a leak can get on a car. No one has ever made a hydraulic system that will not eventually spring a leak.
