I bet you have a rust hole around the hood spring letting water in the rear floor. I had the same problem a year back, I JB welded a piece of metal over the hole and then painted it and then I put a coat of truck bed liner so I wouldn't rust out again. You can't even see the repair since it was so far back in the little tunnel where the hinge connects to the body.

As for the rust in the trunk spray some rust stop on it until you get around to painting the whole car. Maybe that will slow down the rust.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg