There's been many times that guys have had their parts scanned for oil use. I think Chris Bennet did it, and guys like Brad Hollibaugh too. They remain adamant that they do not have any oil in whatever suspicious part.
They then have a test of some sort done, Flex had an MRI on his calves I think, and oddly there is never any signs of oil anywhere. Some of the "experts" in the BBing world speculate that the oil is metabolized, but since the muscle is already stretched the oil is metabolized in some way, shape or form and while the muscle maintains its shape there is no evidence of something exogenous being there.
I think it was Chris Clark who "invented" Synthol aka Pump N Pose or Eskiclean (SP?) There is an article I have in MMI where he talks about it, and aside from the obvious things the oil does to your muscles, the ramifications (even by the man who invented it!) are little known. At least when the article was printed a few years back.