Soak it in Lacquer thinner, requires a weight in the bath......

Soak 24 hours...leave at room temp. as more oil bleeds out, then re-soak for a few hours, then repeat the process......

For heavy oil contamination: If you live in a sunny climate, rotating in the sun helps the old oil migrate to the surface, if not your climate use a heat lamp.......soak and repeat this process as the oil continues to surface.....

Best,

Doug