Just heard word from the shop. Apparently there was nothing actually wrong with the radio, it just wasn't getting enough power. I was not aware of this, but apparently the old RT-328s need almost 14V to work properly. All of the trouble shooting we were doing was engine off or engine at low idle (<1000 RPM). It appears the radio wasn't getting enough power at those conditions. The problem was repeatable when the avionics shop tested the radio engine off. Idling above 1,000 RPM, it transmits/receives fine. They said that's about the best I can expect from the old radio. The MK-12D goes back in at the end of the week. Hopefully I can find a new o-ring from the fuel primer before I go back up there but even if not, it's no biggie. The biggest problem is getting a ride back up there!!
