My old KT-76 Transponder is acting up and during my last flight the reply light stayed on for a usually long period of time. When I landed ATC informed they didn’t see me as I entered their airspace. I’d like to get a few more years of life from the transponder (and avoid the replacement expense), so I am looking for recommendations for an avionics shop that will repair/remanufacture the old KT-76A transponders. Unfortunately most of the shops I have checked around Las Vegas seem reluctant to work on this old model (mine is 25+ years old) and are more interested in selling me a new replacement transponder.