I was at a td at goodwood last year that was cancelled by the management because it was too slippery for bikes ... and he said it was because of all the crap the _cars_ leave on it from their fuel additives and water additives not just their oil which stayed _in_ the track surface for several days after a meeting
It _was_ damp, and not clearing very fast, and a complete **** did plough into the chicane way too fast for the condidtions, so it didnt seem a bad judgement actually.