I have read and seen this question asked and ansewered on several sites. There is no good answer because no one will publish a expected life expectancy on a piece of electronics. Have seen guys post that they have units in excess of 2500 hr's and still work fine then you see units that die in the 4-500 hr range. My opinion is how much vibration and rough handling unit has endured leads to how long they will last. Vibration is probably biggest killer of electronics. Problem is your not ever going to know that.now if you found one where a guy took it off every time and stored it in a protective case I'd bet on it lasting a long time. I also think if you found one in the 3-400 dollar range it would be worth buying. Remember that unit is now really old technology even though they are good units.
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Charlie Weaver USN/ENC 1965-1979