I'm not suggesting one oil or another oil but I do know that some of the bikes we get in for a service at the bike charity I work for have been religiously lubed with sump oil. Let's just say it's the blackest, thickest coating of gunk you could wish for. It takes an absolute age to remove and everything else on the bike (chainrings, cassette, front mech, rear mech and so on) is gunged up too. It even gets in the freehub on the rear hub and stops the pawls from releasing. This has to be shifted before we can even work on it. If it was up to me I'd refuse to accept the bike for service but we're a charity and we take on any old crap. I don't oil mine but I do occasionally drop a few drops of 3 in 1 oil on the chain and wipe with a cloth. I use GT85 most of the time and wipe off any excess. Seems to work.