Coolant leak
 

I've got a head-scratcher going with my 1999 986. I noticed a puddle about 10 inches in diameter that appears to be coolant. I have had no overheating issues at all. and the puddle dried up. I don't drive the car every day, but the puddle returns maybe every third time I drive the car. I checked the coolant level in the reserve tank and it was down slightly, so I filled it back to the "max" level, and after another puddle a few days later, it was down slightly. If I had a bad water pump, wouldn't I get a puddle every time I drove it? I took off the access panel behind the seats and the water pump doesn't show any signs of leakage, and I ran the engine and everything sounds good. TIA for any ideas or suggestions