RE: 300E WATER LEAKS
Thanks to you who sent in helpful ideas. FWIW I have eliminated the sunroof drains; the carpet under the door sill does not get wet, but I will check the plastic door seal; there is a drain from somewhere below the brake booster, I'm told, which may be blocked. My car has no belly pan under the engine. I find no breaches in the firewall other than the grommeted holes for cables, etc.
Since I put towels on the firewall but not reaching the floor, I believe their getting soaked strongly implies water through a firewall opening or perhaps from the above- mentioned drain, which has NOT been cleaned, and I cannot find.
I'm going to try silicone seal to close any leaks through the firewall grommets and finding the elusive drain somewhere beneath the brake booster.