It appears to be surface rust in the trunk of my 76 300D.
My Plan of Attack.
1. Naval Jelly Rust Destroyer and wire brush
2. Rustoleum Rusty Metal Primer
3. Rustoleum Semi Gloss Black Rust Inhibiting Finish Paint.

I plan on using about a zillion coats.
Getting to the source of this water is another matter. The trunk seal is shot so I think thats a good start. However I suspect water coming in around the tail light assembly!

Anyone out there have some tips?
Thanks

On another matter is the horrific discovery of soaked carpet in the front pass. footwell. No, it's not the window seal, that's new. It's a hole in the rocker behind the front wheel. It's been there a while and I'm just dumb for not doing anything about it. (Also pretty much broke til now)
Underneath the carpets the white insulating coating is cracked and you can see the orange brown stains of rust underneath. I don't know if the floorpan itself is hole ridden. Its probably the rocker that is the culprit.
I did some hunting around in the old threads and found a couple things, but I'm no welder of any sort.
Junking the car is not an option. I will do anything for this car.
Anyone know a link to a good thread for novices on how to deal with rot? Aside from cursing it and declaring war.
I hate that losing the battle feeling.
Thanks very much.
Josh

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

Hi Josh,try doing a search for 'rust' or 'water leaks' . Your plan of attack sounds right and in non-structural areas you can use fibre-glass as a cold repair method.I filled a similar wheelwell hole on my 123 with a toggle-bolt and some tin .Shhhh...don't tell anyone .

__________________
Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight

You might want to take a look at a product called POR15. Do a search on the web for it. They make all types of rust restoration products and have had excellent reviews. They are not cheap, but better than Rustoleum. Check it out. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

Thanks guys
Just ordered the POR15 starter kit for 20 bucks.
It does look better than rustoleum, we shall see.
I should've posted before I bought that other stuff!

__________________
63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

MetalPrep is much cheaper than Naval Jelly,,,,and very thin.. it is probably the same active ingrediant... Phosophoric Acid... but you can spray it into cavities .... instead of having to place it with brush... so you can keep your working hole smaller in tight places... go to an automotive Paint pro shop...way way cheaper....been using it for 25 years...
But I think the Por15 will have to be brushed on .. it is the toughest stuff , once you have a clean surface, and follow the instructions.... that I know of.... not new either.... been out at least 20 years and used by the Hemmings Motor News crowd....