I've used SEM with success on those parts. Remove speaker cloth if spraying that area.

http://vinylpro.safeshopper.com/29/cat29.htm?582

Many of the wreckers yards use it in my area to make a part the right color if they don't have the correct color in the yard.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)