My Mercedes SLK 250 won't unlock. Last Sunday it sat on my drive during very heavy rain and hasn't let anyone in since. The key raises the button but the car remains locked. Both keys have been tested. I've tried various tips from local experts and everyone is baffled (eg giving it five secs plus with the key held close to the handle to send an infra red signal). A mechanic jacked the front up and declared there was life in the battery. I'm about to get it spec lifted to the main Merc deal which my brilliant local garage said was probably best in case they failed to solve the problem. I reckon its to do with water ingress. This might be irrelevant but a few times the aircon hasn't switched on which I also think is after heavy rain. It makes me wonder if some filter is sodden or unseen gutter blocked and could this now be causing the car to lock down?