Not sure if this is the right place to post, but here goes... I have an M62 Supercharger (the one with the clutched pulley) - i have it off a donor car and i took it apart to check it's condition before i install it on the car. Donor car had about 200k kms. The snout is in good condition (no play or leaks), the rear needle bearings need to changed, the existing oil is kinda ok - it's an amber color, no sludge or particles in there (managed to recover around 100ml - will put new oil in).

However i have one issue : the front rotor bearings are in good condition (no play or noise whatsoever). But there was a small film of oil on the rotors and on the inside of the case. The rotors themselves are doing really well, very few (and minor) scratch marks and the teflon (or epoxy) coating is absolutely intact.

So i wanted to ask you guys, is the oil on the rotors supercharger oil, leaking from the 2 seals? Or could it be oil from the engine that got into the supercharger via the PCV / recirculation system? I'm going to change the rear needle bearings (seems like simple job - i have the tools needed, press and pullers), but the 2 front bearings and their seals look like a major headache (taking them apart won't be that complicated - what worried me the most is putting everything back together as the tolerances are minimal). So if the leak is from the seals, i'll try and change them (and the front bearings as well since i'll be taking everything apart). If it's oil from the engine (i have checked the intake pipe section and there's oil on it's inside as well), i'll just change the rear needle bearings and oil.

Is there any way to test if the seals are leaking?