Hi Mike ,---- My wife's 98 C230 does the same thing after a heavy rain or car wash.Take a look at the 2 drain holes, the are half-moon shaped & are only positioned at the very front & rear of sheet metal roll over lip. No drain hole in the center, plus both holes are approx 1/8 " above the bottom. If the car is sitting on level ground it builds up, when you open the doors, it disturbs the level & the water comes gushing out. About twice a year blow the drain holes with compressed air , driving up & down hills will keep the water drained . I think they are functioning as designed.------- Ray