Went to hop in my E350 BlueTEC this morning after a pretty severe rainstorm in the early hours this morning and was greeted with this very unpleasant sight. It's dirty rainwater, not coolant, so that's at least some relief.
I've driven this car through several whiteout rainstorms over the past week and it has sat outside uncovered in a good bit of moderate rain and hasn't had any hint of leakage those times.

I checked the rest of the cabin for dampness or puddles and didn't find anything. The door seals don't appear to be leaking (no water trapped between seal and door frame, and the sunroof and headliner are dry. No water on the dash.

I bought the car about a week and a half ago, so I can't testify to its upkeep beyond regular scheduled service indicated on the CarFax report. Is it possible that a clogged body drain could have overflowed into the cabin somehow?

Attached Thumbnails

 

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)