15 years later...
My 1993 oldsmobile cutlass supreme sl has the exact same problem. All foot areas are wet and most water is in the rear passenger side's foot area. Water enters when it rains. Car is parked facing uphill usually.
I sealed my moonroof with sealant, but I checked during the rain and I see a little drip drip still coming from the rear drain hose (4 in total). I think the water rises faster than that.
I'm that horrible 25 year old who has allowed to remain wet for over a month (I vacuum water out sometimes). I'll update this thread when I figure it out.