This is starting to get old. I've done this on two of my 300Ds already. I wire brushed the paint and rust down to bare steel with a bench grinder wire wheel. I have tried various spray paints from different manufacturers without any luck of having the bolts remain rust free for more than a year. I only use a torque wrench on then and no harsh chemicals. Short of powder coating, what can the diy guy use/

I can't imagine any paint that would hold up to the effects of a socket when it is torqued against the finish. A galvanize or zinc coating would probably work the best. No, I don't know how or who would do that. Sorry.

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95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K

I run a shop here in Jersey. We do powder coating.....I did my lug bolts on both cars ....there rusty. Even the jack / wheel assembly on my trailer. Rusty!
I sand blastet the jack and sprayed it with rut-0-leum primer and black paint out of a can......3 years ...no rust!
Powder coat dont protect aginst rust.....

I've tried About every brand of primer and spray paint in the store. It can't be the salty winters in WI, I don't drive that much in the winter. I'm getting down to bare metal. What paint process does Mercedes use? Do I have to touch up the lug bolts every time I rotate the tires?

I wish that the people who make the chrome caps (made of plastic) would make them in Mercedes silver. This would conclusively solve the problem. There just isn't any paint really sturdy enough (although I have seen plastic-lined 6-point sockets made just for this problem).

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86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm