Clutch metal plates, black marks

[Shammon]

1977 Goldwing project going ok so far, Engine about to go back in but decided to replace the clutch just in case it was bad.
Glad I did as the friction plates were worn and I noticed the metal plates all had black stains on them.
The metal plates were not blue marked but it looks to me as if there may be burned? I intend to replace them all as to me they look
as if they are not right cant take the risk, Any advise welcome as to what has caused the black stains and if correct to replace or clean.
The middle thicker plate B is fine rivets still strong and no stains. Stains not easily removed on the plates when I tried steel wool.

[Fred Camper]

Might be an issue with the engine oil that was once used. Since they do not clean with steel wool I suggest they remain usable. But as I have not noticed that before my expertise is limited.