Ok, so that you know .. there is no common o-ring that leaks oil on the supercharger internally. At the pulley end, there is a seal, that seal can sometimes leak, it's externally though and that is easily seen on the belt and snout. No engine oil enters the supercharger. Turbos do have oil seals and are prone to leaking and burning oil.
I'll repeat that, no engine oil ever enters the supercharger for lubrication of it's parts. The only thing that enters the supercharger is oil vapor through the pcv. The pcv should have an o-ring on the bottom of it, then it goes in, then a spring and the top cover. If that o-ring wasn't in place you should have a vacuum leak and possibly a whistling noise.
