I have only had one fail and it was the remanufactured one that I installed "just to be safe" It was on a slant 6 and it spit the gear off the drive. I ended up putting the old one back in. That being said, if you're going to spend the money for a complete rebuild, a new pump from a reputable supplier is good insurance. As far as how long they last.... that really depends on what they have been pumping. You could take it apart and make sure it isn't worn or scored.
Oil pumps are one of those parts you don't want to know how long they last. If you have any doubts at all about it, replace it. Like 300 said,they're 22 bucks. It's cheap insurance for a long lasting motor.
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