2005 Mercury Sable relays

Relays on this car keep going bad. So far I have changed wiper, fan, starter, and fuel pump relays on this vehicle, relay module is mounted in front of vehicle. Could this be a problem with moisture or a bad voltage regulator. Car is running fine now, but some times when I turn the key, is is dead but will start after a couple of key turns. After changing the starter relay. It's fine for another 1000 miles. Whats going on