Tom,

Since this happens at  odd times  with long periods between events, I'm 
not sure I would start doing major changes "just in case".

Fire up the radio and start jiggling  coax connectors. Between radio and 
amp, amp to TW-1, and TW-1 to tuner.   So there are 3 jumpers and 6 
connectors to play with.

I would check the voltage  on the power supply, but I seem to remember 
that  a few times over the years when you had  a problem and suspected 
ps voltage, it always turned out to be something else.   Bad jumper one 
time if I recall.

If the problem returns,  connect your dummy load or antenna  direct to 
the radio, see if RX comes back and check swr using the  Kenwood's VGS-1.

I think sending it out for service at this point will just result in a 
"no problem found" reply as well as loss of radio time and shipping 
costs.  You can always box it up and send it here, I'll be happy to 
evaluate it for a few months n/c.

73, Steve KW3A