slant 6 main bearings

I know
surface of the coating has oxidised. you catch you finger because the oxide takes up more space than the original coating....

metal polish and a soft cloth followed by a very good clean.


Might work
your engine

Dave
I know what you mean but I'm my case there was splinters of whatever coating in the package when I opened it up, and flaking off some of the shells, whatever it was was a hard coating of some kind, dill gray on the outside and black on the back side, shells where coating was missing was same flat black as back of coating remnants. Cheaper to buy another set for piece of mind