osprey - if I was going to the Hebrides I wouldn't want to discover that any fix had only been temporary.
That said the two common and easy to fix issues with all fixed VHFs are: (i) poor power connection which means it never gets enough amps to transmit; (ii) dodgy ariel. I expect you'd get some transmission close up though even with a bad ariel, so I'd certainly look at the condition of your wiring.
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