Bill,
I am not sure if Brian has sold the business however I spoke to them a couple of weeks ago and was told Brian was semi-retired from the business. So not sure if we will see much of him in the future.
Also I had my starter motor changed by Brian 2 years ago, for a year or so no clicking but it does return now and again, usually during colder weather. If I take the car out at least twice a week this also helps. Some of the advice I have heard suggests a small film of rust coats the starter brushes when the car is not used often. Also poor earth, worn starter brushes, cooked started motor are other possibilities although these would be more likely on an original starter motor. Someone had a very different problem some years back, the switch on the clutch pedal which opens the starting circuit had cooked. This results in no clicking at all.
The fast paced clicking I experienced was on a dud battery some years ago.
The clicking I believe is the solenoid on the starter, firing the onion into the ring gear. If the battery is still good it resets ready for another stab at the starter button. If the battery is dud, the solenoid circuit closes pulling the onion from the ring gear then fires again with no amps to turn the engine and this process keeps going while you have the button pressed.
Dave