Chuck, you are a one-man statistical data source!
All I can do is relate my own experiences with flying.
As a rough estimate, how many times did you decide not to fly at all because of pre-flight doubts about the engine?
Just off the top of my head I can think of three engine problems I had that were enough concern to persuade me not to fly them until the cause was found.
The first time was with an airplane that had had an engine failure and the crew had to use METO ( Maximum except take off. ) power to get back to the airport.
They changed the failed engine and I did the next trip on the airplane, on descent the other engine started to backfire as power was reduced at the destination and also when returning to the departure airport ( Goose Bay ).
The decision was made to change the AMC in the carburetor ( Automatic mixture control unit. ).
On the test flight it had the same problem and we started to look deeper into the issue, I happened to be coming back from getting some stuff for the job and they were running it up and listening to the sound from a distance I had a hunch what was wrong, cracked cylinder ? 's.
We did a leak down test and there were four cylinders below specs.
We changed four cylinders and on the test flight I was looking at the engine as the power was reduced from climb power to cruise on the down wind leg...as I watched a cylinder let go and went right up through the cowling, I just hit the feather button and then followed the feather shut down check list.
The engine as I had suspected was junk and my decision not to fly it because of the way it was acting was correct.
That was the first, should I use more bandwidth and relate the other two?