You can buy DOM-16 at NAPA Canada. It is a similar product to POR-15 and Miracle paint, except about 1/2 the price. I used it extensively when I restored my 300D.

To get at the floors, if 240D is same as 300D, you will need to remove the sound insulation - it is a tar like material that is adhered to the floors. Had to use heat gun to soften it up so it could be scraped off.

It's easy enough to get the seats out. You will want to get the lower dash out too as well as various other pieces of trim and conduit covers that run on floor. That will let you see how bad floors, sidewalls and firewall are. Small holes can be fixed with DOM & glass. But if, as I had, there are major rusted sections, then some welding will be in order. You don't need to necessarily buy floor pans unless the whole floor needs replacing.

With side panels out, you should look up high on both sides at area around firewall and just aft of that. That is where holes from hinge pockets rust through. Also check where hand brake bracket attaches to firewall. Mine was OK.

If I were you, I would dig as much as possible to determine just how much needs repair. Only then make a decision on whether to proceed or not. I went ahead, but did a great deal of work myself, after the welder had done his part.

When judging whether a restoration is worthwhile or not, many of us look at what the car will be worth once done. I do that too. But in the end, I decided three time on major repairs on our 300D, more based on how long I would extend the life. A $7000 engine swap in 2001 (still going strong), $3000 repaint about 7 years ago (still good, but needed a couple of touchups) and more recently $3000 in rust repair. But car now will hopefully be good for another 5 years. But not unless they stop putting salt on roads (freezing rain coming tonight )

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5