I thnk the one in my '85 is original, nearly 280K miles and pressure is still good. I do carry a spare in my parts box just in case. I thnk they last a long time as long as you don't run them dry too many times. That is probably the biggest killer, the pump uses the gas as a coolant and lubricant.

r.c.brown@ieee.org
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Project: 4Crawler
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