Coolant Mystery

[murzzo]

Reversed my 2003 RX8 231 down my drive. Walked over to close my gates, saw a trail of water leading to my car. Looked underneath, sure enough, water flowing at a steady trickle from aprox under my gearstick. As it was getting late, and i had a bottle of vodka waiting :guinness, i put the car to bed.
Next morning, filled the expansion bottle up, let it run through etc and filled again. Took it to some mechanics, who searched everywhere, no sign of a leak. Hasn\'t lost any water in 2 days now. Ideas ?