Decided to clean the interior for the first time since purchase. On lifting the passenger side floor mat I found a pool of green 'radiator water' which appears to be coming from the heater core. After some testing I discovered that if I leave the A/C in COLD position it doesn't leak, living in sunny Spain this is not too much of a hardship so I am not going to attempt to fix it for now. The temp gauge is always just below normal so it must be a small leak. Is this a common fault on early models equipped with aircon?