Make sure that your AC system is dripping the excess water out the car. If your drain tubes are blocked or partially blocked you may have water in the heater box and its adding it to the car when you run in EC.
How humid is it outside? Your in the Bay area and if its humid this may be normal. Does it occur on a real dry day, if thats posible in the Bay area!!!!!
I would check you AC drain.
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car