the other day i noticed a flake of aluminum coming off the top of my valve cover. the flake was very thin, but it looks like it could get larger and im afraid the problem could get worse.

is this from cold water hitting the cover while its hot? thats what i would guess. is there something else that could cause this?

is this a serious problem? the flaking seems very minor right now, but could it get worse? how could i prevent this?

thanks for all your help.

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1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350