I'm surprised that your MX-300 failed so quickly. I had an MX-385 (24V version) in my former 152 for about 15 years. On average, it needed some kind of "tweaks" (bad squelch, static noise) every 2-3 years. Back then, TKM still serviced them, for a fixed labor cost of $95 (one hour of labor) plus any parts. Sadly, they have a "rolling" range of serial numbers that they no longer service (based on manufactured date) and my radio eventually got aged out in 2016.

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