We have a scratch in a door about two feet long, one eighth inch wide and through the first layer of paint. No metal denting or creasing. Is there a satisfactory way to repair the scratch without repainting the entire area?

Take it to a professional body shop, preferabbly a Mercedes shop. Things like GT88 just don't work, not even on hair thin, hair deep scratches. An MB shop will be able to match paint exactly, and may be able to do it without doing the whole door. The reason most body shops seem to charge so much is that they probably don't usually stock you exact colour of paint, so they have to order a paint kit. Even the smallest size paint kit may be way too much paint for your job, but they have to buy it and you have to pay for it. A Mercedes shop might have half a kit or more laying around that matches your paint. I had the rear wheel wells and an area around the gas cap re painted (and some rust sanded off)on a car a Caddy I used to own (technically I still do own it, but somebody stole it from me and who knows where it is now). The Caddilac dealer did a really good job, you couldn't tell it had been repainted. They charged me only $200 Canadian. You might be able to get it done cheaper since it is a smaller job. I think it is worth it to get it done right.

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Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired

If you want perfect, you've got to go to a quality body shop. Usually chips can be repaired without having to repaint the entire panel. A long scratch must be repainted. The scratch area needs to be sanded and color coated, then the entire panel must be clear coated. They key is going to a high quality shop in your area. Get recommendations from other car people and check out the work first.
Good Luck.
Gary

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00 Silver/Black AMG E55
96 DCM Impala SS
94 Admiral Blue ZR-1
81 Candy Apple Corvette Cpe

If you really want to save money and do it yourself, it really isn't that hard, it does take some time though.

Basically you need to set a weekend aside to do it right.

Checkout this link for the whole process in detail, http://carcareonline.com/howto_articles.html.

While I agree that some people can do repairs themselves and save money, you can also make the problem worse and sand off the clearcoat. For a first-timer, these procedures should be tried in an inconspicuous area! If you are satisfied with the result, than go for it! But, like I said, for perfection, a high-quality body shop!
just my $.02
Gary

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00 Silver/Black AMG E55
96 DCM Impala SS
94 Admiral Blue ZR-1
81 Candy Apple Corvette Cpe