Well, many of them are that's for sure. A mate bought a fairly old VW Transporter to convert from a panel van into a weekender bus. Much of the outer bodywork was tatty but the previous owner was a gearbox mechanic so the entire floor was covered in a gritty thick grease, and once scraped up and the whole lot degreased, it looked like new (as was anything it had seeped into). ;-)
No, I remember something similar as well. I had one vehicle where it was vented into a bottle and I could pour it back into the crankcase now and again. ;-)
Cheers, T i m