Kyle:

I don't know what it is, but it is great stuff. Same as Volvo, I think (white on the volvo) and simply never goes bad. All the rust I've seen so far on MBs is from badly sealed seams or water standing in the interior, almost never see rust from the outside, at least on the newer models.

I don't know if you can weld through it or not -- you can always grind some off if you need to. See if you can get some from MB for re-painting, too -- probably expensive, but far better than autoparts store stuff.

Get some seam sealant, too -- the stuff MB uses to fill body gaps. Wonderful stuff, stays flexible like their undersealant but thicker.

If you are replacing lower fenders, get the tool to make an offset to set the new panel in -- we butt welded the homemade panels here, and it is a pain. Much easier to make the offset and drill/plug weld the new panel in place -- less heat and less distortion. Fill the inner side with MB sealant and lead fill the outer if you can -- if not, Bondo will do, but lead is better.

Have fun!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!