2005 Mercury Sable relays going bad

The problem is the relays mounted in front on top of the rad keep going bad. So far I have changed both wiper relays, and both fan relays. The last epesode was when the car went dead and had it towed to the dealer.. They found the anti theft had disabled the car and the fuel and starter relays were bad. Had to reprogram the computer and change relays. This all started after I changed the fuel filter. [A coincidence, mabe ], a couple of months later, again the car would start onlly after turning the key after a couple of tries. Sometimes it would take five minutes. Thinking about the last time this happened, I went and purchaced a new starter relay. This solved the problem. Now the car is running fine, for now, but I would still like to know what the root cause is. Dealer can't find a problem. What's up, do I have a lemon.