Check to make sure the gasket for the trunk is clean and not torn. They usually don't leak even in bad shape UNLESS there is something either under the lip or hanging across the seal, in which case water will drip into the trunk. Rotten leaves, grass clippings, twigs, etc tend to build up in there, and when they fill all the space between the deck lid and the body, water gets in.

Also, make sure the water drain channel down the sides is clear, no piles of pine needles, leaves, etc. If water cannot drain down and out, it will work it's way past the seal eventually, causing a wet trunk.

I've been told that there is also a weather seal around the rear window that can cause trouble, but my damp trunk on the W124 was too much crud under the gasket. Cleaned it all out and it stays dry, now!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!