Water leaks, '89 300E

In my '89 300E water leaks into the driver's floor. I have covered the windshield seals with caulking, hoping that the windshield, the usual suspect, is the source of the leak. No luck. Perhaps I didn't seal things right but I tried to cover every inch of the seam where the rubber meets the glass.
It leaks only when driven through a heavy rain: it will not leak if left in a down pour for hours. If further tests of the windshield still don't find a leak, can anyone suggest where on the body there might be a leak? From what I can see, all the body drains are clear and no one can find any place in the firewall where there might be a leak.

[vinamg]

I am puzzled by "It leaks only when driven through a heavy rain"

I would check the following:

1. Sunroof drain (if you have a sunroof)
2. AC evap drain (I know you only mentioned rain, but just to be sure)
3. Remove plastic channel above brake booster and thoroughly check for rust.

Vinamg

[ymsin]

"It leaks only when driven through a heavy rain: it will not leak if left in a down pour for hours."

If this is what you find conclusive, then you may have to check 2 places.

Hoist up your MB and look for holes undercarriage, esp at the area where it leaks. Don't discount the firewall at the proportionate area where the leak is found.

If it was an uneventful search, then you might have to check the skirting where the door closes onto the step. There could be a gap where water may be seeping in - more so when travelling but not stationary. This is a wild guess.

I would go for the hoisting up, thus you would get a very definite clear picture of whats lurking beneath.

All the best.

FWIW I've found the leak. There is a hole beneath the kick panel on both sides, at floor level behind the carpet, and partly hidden by the electrical conduit box. This is an oval about
50 cm x 30 cm, a little behind the drain hole in the bottom rail, and allows some wiring inside from the bottom rail . This hole is much larger than the wiring and has no gasket or cover. The local dealer parts counter is sympathetic, but they have no such part. The inside of the rail is coated with gritty grime that has been blocking the small holes in the drain hole grommet, causing water to back up and flood the floor. This grommet has been cleaned several times but I suspect it has been blocked up again as soon as I drove long enough through a hard rain.

I would be interested to hear from anyone who knows what should be filling this hole (surely there should not be an open hole in that place).