My KW TM-732 generates an RF carrier, but does not mix audio all of a
sudden. I have proved it to be the radio and not the mic.

PD-

I had a very frustrating problem like yours with a Kenwood TS-660. With
service manual in hand, I tried making voltage and oscilloscope measurements,
but nothing seemed to be out of order. Not being able to track it down, I set
the radio aside for several years.

Recently I came across it and decided to give it another try. This time I
found that the microphone really was bad. It had an intermittent connection,
and just happened to work when I had tried it on another rig.

73, Fred, K4DII