Almost looks like a bunch of RTV sealant got into the oil and gradually mixed in with it. That, or the owner used some kind of food-type oil, like canola, etc.. and it did a TON of cross-linking.
I think RTV would make lumps, wouldn't get such homogenious mixing up. The veggy oil I can hewr some more about. Would gel a mineral oil like that? Also don't think its thermal stress neither oxidation thinkening on that one...
What about other contaminants like rubber solvents in fuel, etc...