Izzy,

Two eTrex failures taught me one thing. They do not like vibration. A 3 foot bounce off the pavement they can survive. Riding in my truck with constant but small road vibration does them in every time. If you think this might be part of the issue, see if it is possible to isolate it somewhat from the constant vibes.
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I do the things that I must, and really regret, are unfortunately necessary.

RIP OBG