94 Passport 3.2 bad injectors

I had a problem with my 94 Passport 3.2 running rough and the engine missing. I did a compression test and isolated the problem to the number 3 and 5 cylinder. I had to replace both injectors which were shot. This job was a real PITA. My question is what would have caused both injectors to go bad? Does the ethanol in the fuel have anything to do with this and if so iss there an additive to run in the tank to ensure this doesn't happen again?