How can i fix my saab 900?

My 1995 Saab 900 3-door coupe leaks during prolonged rainfall just sitting on the drive! I have a puddle in the rear floor area (behind the drivers side) and also some water under the mat in the driver's footwell. As the drive slopes slightly and the car is tilted backwards when parked, I assume that the water might be entering in front of the bigger puddle on the back floor but I can't make out where. There are no obvious holes in the bodywork or seals. Anyone know of particular areas on this model i could investigate? Any suggestions greatly appreciated.