My daughter just bought a E-320 that had one piece of door trim the wrong color as the previous owner got it from a junk yard. Since the car is white and the trim should be also, I bought a can of white Rust-oleum "Specialty Plastic", a "Direct-to-Plastic-Paint".

It worked perfectly! Their white matched that of Mercedes exactly. Less than $6 including tax. Comes in a variety of colors. http://www.rustoleum.com/CBGProduct.asp?pid=118
They also have a textured and a hammered finish in addition to full gloss.

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles