I think you're referring to Mercedessource.com, which is a great business and very helpful. I have used them several times for parts on my W123 300TDT diesel turbo wagon. They focus on the diesel Mercedes, in general. Perhaps this is from another source though. In general, their rust repair manual speaks about non-welding ways of fixing rust. I got one by accident when I ordered a new factory battery tray for the w123. The battery tray on my diesel wagon was the only piece of rust on the entire car because of corrosion from the old battery. The kit contained miracle paint and this rust repair manual. The miracle paint worked well, but again, I didn;t have rust on the vehicle once ai removed the old tray. I slopped on the miracle paint on the firewall and inner wing near where the battery tray was just to prevent problems down the road if the new battery and tray caused them. Suppossedly miracle paint works like por, it binds to rust and changes it chemically. For a pagoda w113, you want to tackle any rust structurally and remove and use these rustproofing paints to prevent in the future, I think. I think the w113 chassis deserves the appropriate repair for any rust, if you can afford it. This is my opinion. I used it on the diesel wagon because, although it's in great shape, it is my daily runabout car.
-CD-
1967 230SL, 113.042 10
1983 300TDT, 123.193