By chance, mainly because there was a drum of it sitting at the yard and I needed something oily, I poured a mixture of burnt gear oil and disel into a stuck engine, Cleared it very rapidly, a couple of days, as a benifit it also took the rust off. Don't know why, but no old gear oil now goes to waste. By the way, don't Aussies have a tendency to soak anything rusty in Mollases?