Do you sometimes have transmit issues with your NARCO MK-12D through your Garmin 340 Audio Panel? I really like these radios, they've performed well and are now easily found in decent shape on EBay, so I was reluctant to give up on them when these issues crept up.

No side tone sometimes and when you turn the audio panel off (failsafe mode of audio panel is direct connect of Com1 to transmit) but your transmissions are OK but chopped off?

Well, this is the verbatim fix given to me by the NARCO techs that solved my problem:

"There is no bulletin concerning the Garmin 340 audio panel. The work around is a simple fix for your avionics shop to install. All they need to add is a 1K ohm 1/4W resistor from the MIC AUDIO line (PIN N of J101) to GROUND on each of your MK12D trays."