What is the exact capacity of the m90's oil? I have drained as much as I could before and filled with a bottle from the dealer. No problems but just curious.

At least 2 bottles.
It takes a bit more to get to the plug threads, but if done regularly 2 is sufficient.

Just out of curiosity, how often should you change your supercharger oil?????

I have heard anything between 20,000 miles, to 50,000 miles.

To be honest, I have never changed mine (54,000 miles) Should I do right away???

Owners manual says to "check and fill to appropriate level" every 3 years or 30K miles.

I like to change it, rather than just inspect it every 30K.....

I've seen some pretty nasty SC oil come out of a car, but it was over 100K, and car that lived it's life at the coast of the Pacific Ocean. Typically it comes out stinky, no matter the mileage.

That stuff is stinky out of the bottle Two bottles is plenty. Cheap insurance every 30k