Cobber

Get some of theive the offending oil on your finger and give it a good sniff, if its gear oil it should smell worse than a pole cat's arse!
Its up to you if you need to get a pole cat's arse onto your finger for comparison purposes!
I for one am happy to imagine that they don't smell good.
You should be able to smell gear oil, even if you're like me and have had your sense of smell largely destroyed by an industrial accident (chlorine gas spill)