Wow!!! Have I been chasing my tail!! Additionally, I have been asking for help without giving enough information. So, here are the fact as provided by some logical diagnosis, along with a discovery. This took some time, as the condition is intermittent, and once the engine spins up nicely, I have to wait until several hours later to make additional tests. You guess it, it has been an all-nighter.
I first spun the starter by applying 12 volts directly to the starter positive lug. The results were that it spun up fine; no problem. That eliminated the starter, and the sprag clutch.
Next test; I placed a jumper directly to the starter solenoid coil circuit ( the small push-on post). The solenoid did not buzz. It offered solid clicks each time that I applied 12 to it. Again, no problem. Starter solenoid looks good.
Next, I went back to the key switch, master on, ignitions off, and I got the prop stall, and buzz from the start relay. Only this time, I happened to be looking at the key switch, and noted that the spar pin light was flashing intermittently, and in time with the starter solenoid chatter. After a few seconds the spar pin warning light remained off, and the engine spun up just fine. Bottom line, the problem is in that spar pin circuit somewhere. It isn't on when I turn on the master, nor has it ever come on in my 120 hours of flight. Only during a start attempt, My problem is that from here I am lost. On the schematic, I see a relay, but I have no idea where it is, or what is causing it to chatter during start, but that is the only way that I can see to flash the spar pin warning light, and interrupt the starter solenoid pick circuit.
I am so excited to know that my problem is not sprag clutch oriented. With some help from you guys, I am certain that I will get to the bottom of this.
Thanks, ever so much for your thoughts..............Tom