What you have marked is NOT bare aluminum . I do know the differance.

meh believe what you want.... its not worth argueing

I still have full boost end of argument!

You have what you THINK is full boost because of the colder (denser) winter air. You do NOT have full boost because of the coating loss.

You posted here in this topic on our Forum for help and advice. We gave that help and advice to the best of our ability based on our VAST collective experience with these superchargers.

You can take our advice and help or not. Your choice.

END of argument.

15 deg c warm enough?
I have a vast experience in coated metals, I have sent out many form ,flange and die steels for recoating of ALL types and have done MANY repairs over my 25 yrs in the trade.

What you have marked up in the pictures is NOT BARE METAL .

Okay, I Too, have pulled my supercharger apart. It has the Epoxy Coating, which, is that blunt grey colour.
My rotors look alot like yours, missing some of the epoxy coating, it wears off over time im sure, and at 139,900 kms..it is..on my car..
The Rotors are highly polished beneath that Epoxy coating, I can tell you this because I pulled apart my M62 Gen 2 (no epoxy from factory on Gen 2) Heres what It looks like

Left Lobe was washed and has 0 Epoxy coating on it, it never did.

These are the rotors out of my 97'* M90
Lightly cleaned with citrus.

What you are looking at on yours is indeed aluminum,however, its got some crap and fragments of epoxy cooked onto its surface,Thats all thats under the epoxy, nothing else.

Maybe someone should post some rotors with no loss to compare.

Can do, but I have issues with arguing topics with people who are in argumentative denial and think we know jack ****.

I'll post some pristine rotors from two different types of eaton blowers later tonight.

Just do yourself a favor and don't try to clean anything else off your rotors. Even some carbon build up helps seal up the rotors and increase boost.