Echelon

Hi there,

My car: 1996 Ford Escort Cabaret, 1.6 Fuel injection, induction kit, different exhaust.

To cut a long(ish) story short, it seems the O2 sensor in my car has gone. It's quite corroded inside the plug, and the insulating is all coming out as corroded powder. The plug is screwed in such a way it won't reconnect now.
I'm not too 'up' on cars, but it's the O2 sensor at the front of the car that connects to the engine?

Anyway, I've called a local mechanic who's informed me that under no circumstances should an O2 sensor 'break' like that, they should last indefinitely. Logically I don't believe this, as everything has a life span, particularly mechanical parts. He told me that if a sensor breaks like that, that it's quite possible that it's caused by another problem - such as fuel getting into the sensor and corroding it, or some other potential issue with the car. Is this true, or are they just looking for more things to bill me for?

Thanks in advance.