Not diesel specific I know, but IMO this is the best section of this site.

I am doing some rust repair in the floors of my 240D. Part of the problem was water getting in between two layers of metal on a factory lap weld. I am replacing the rusted out metal with factory sheet metal and am keeping the factory design with the lap weld, but would like to be sure that the rust will not return in this seam. Can anybody think of a rust proofing product that will stand up to the high heats that will be occurring when the joint is spot welded back in place, or that would wick into the seam after it has been welded? I have considered pouring some oil into the area after welding, but want to explore other options to make sure that my undercoating, seam sealer and paint will still stick to the area when I apply them.

Thank you for any suggestions.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine