Ha! It might be condensation, but PROBABLY NOT, especially if the carpet is wet!

I had this issue with all three of my 240Ds.

The guys have summarized it nicely.

1. Crawl in the trunk with the flashlight and with your friend/wife on the outside with a garden hose (and the willingness to let you out when need to escape!). That will tell you a lot about where the leaks are, (and whether your friends and wife love you).
2. Look for rear window seal. It will typically leak around the corners of the window where it drips down into the trunk. If it is this, you will need a new factory window seal and pay a glass shop to R&R, as noted. If you have damage to the seal channel, you might need to do rust repair on it.
3. Check the trunk seal itself. If it leaks it will be obvious. Again, I recommend a factory seal, they really are the best. You'll need to be careful, make sure it is 'bending' the right way, and you'll need to use glue to cement it down.
4. Also look at the rear tail light seals. These are also available from the dealership. These are the easiest to replace.

The rear window seal and the trunk seal are both around $170 each.
The tail light seals are around $45-50 each.

If I had to blindly guess, I would say the rear window seal. People always miss that. They don't realize that if it is leaking, it leaks into the TRUNK.

Good luck!

Packman

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83 240D - 4 speed manual - Manilla Beige
189K miles, Tachometer mod, cool wooden shift knob from PeachParts, CocoMats, Original factory paint, manual windows, manual sunroof. Starting to add AudioWrap to this car too!