STOP PRESS - problem identified!  @skipperT - Wanting to be thorough and rule out all possibilities before buying a new starter motor and getting into a tear down of the bike, I thought I'd use the time proven crow-bar method of bridging the terminals of the starter solenoid to rule that out as a possible problem as per your suggestions. This pic is out of the service manual - First, I tried again with the starter button/switch and got the now familiar solenoid 'thunk' as