My 1977 Mercedes 250 W123 sedan has an annoying problem that I cannot solve. Whenever there is heavy rain, water finds its way into the cabin and wells up on the right hand side rear passenger's floor. Please note that this is the REAR passenger's floor, behind the driver's seat - RH drive). The car does not have to be moving for this to happen (i.e. water comes in when the vehicle is stationary). I thought maybe it was coming in through the door (somehow) but I can't feel any moisture on the carpet between the door and the floor. Any ideas?

Take the panel off under the dash on the side that is leaking, and the carpet out of the front floor area. Then lay under the dash with a flashlight while a friend sprays the car down with water. Pay close attention to the windshield gasket area and for rust holes in the firewall.
Hope this helps.

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MB Medic
14 year MB tech
7 year shop foreman @ independent MB/Volvo shop

I have same problem ---in my case it is penetrating back window seal---running underneath back ledge--- under back seat back ---under back seat base---and onto floor in back seat area---a good way to check if you cant find a hard to find leak and if you have bare metal(behind seat back) is to mix a strong paste of artists water color paint horizontal line let dry ---spray car with water ---any water penetration will wash line away indicating where leak is---afterward the water color can be wiped off with a damp rag---syd

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syd 81.300SD.200k
72.300SEL 4.5
mileage.Only god knows!

also check that the hood hinge drain is open and clear, besides rusting out the hood pivots, a remember a car that held so much water in the hood hinge trough that it would spill thru a body seam, down the firewall under the carpets and puddle up in the back. The front windshield leaking or disconnected ac drains also can pile up water in the back. When I find standing water under the rear carpet I always look under the front carpet first!!!

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My 77 123 had the same problem, I cleaned the front drainage tubes from the vents in front of the firewall, and resealed the rear window, and all was fine after that. I'm sure if you look at the 22yr old rear window seal, you'll see plenty of cracks

regards

Russ