Now that I have the floor rust repaired and am trying to figure out how to bend new metal to fit compound curves in the wheel wells, I suddenly find gaping cancer holes both ends of the underbody just below the taillight pockets.

I can look up through the one on the driver's side and see the taligate sill from the underside.

Also, the entire edge of the ledge that meets the top of the bumper is rusted accross its entire length.

It is all hard to get to because the holes are way up above the bumper shocks.

There is lots of surface rust, too, so I think this may have rotted from the outside - in. Is there an inside-out (downward) path?

I can't see anything from inside the cargo hold nor in the spare wheel wells to indicate such. Both cargo panel widows were leaking for who knows how long. Could they be the source? If so, where it the path the water took?

With no torch or plasma cutter available, what tool can I use to reach up there from under the bumper and cut howizontally to remove the cancer?

I have exactly this problem on my '86 245. Just went to Maaco and was told it would cost 350-400 to have them fashion a replacement piece, weld it in, & paint it. Mine is totally rusted through, by the way... resulting in nice holes to the cargo hatch.

This is a common area for rust on all 240s wagons and sedans. There is a seam here a lip. where the uppper body sheet metal meets the under body sheet metal.

On older ones with the big bumpers, the rubber that runs along the top of the bumper and fills the gap between the bumper and the body has a channel that slips over this lip of a seam. this channel traps water/grime/salt and eventually begins to rust the seam. Holes of this sort make the car dangerous because exhaust fumes are sucked back into the car.

This-like the licenseplate lite holders that chip the paint and cause the car to rust at that location- is just one of the 240's weak points.

you have to take the bumper off to fix it right

Right!

you summarized the problems precisely.

Now that I have the bumper off, i can see what is happening. I am surprised it is a fault with that horizintal seam. I would have guessed (and I should not guess) that it was a leak in the roof or hatch hinges someplace.

But the widespread nature of the rust and its intensity tell me it is the seam that failed.

Any ideas about how to get some kind ot rust repair inside of that channel?

A couple of things happen here. First is water gets trapped at the bottom of the tailgate rubber seal and makes a few small holes, once this happens it is not long before it starts to come out of the other side. The second is that '86 and on 245s have that piece of plastic that directs surface spray, grit, rocks etc. onto the bottom of this area. These two things tend to meet in a big rust-fest in the middle and then start dumping water into the under floor compartment.

To get better access, just take the bumper off.

Andrew