Many thanks, kingsolmn & ryck. Feedback and insight always welcome. I have been trying your recent suggestions, but alas, no joy.
In poking around the web, I have found a few variations of the fixes you propose, but have not (yet) discovered a true fix. I suspect (guess) that is because there remains some uncertainty re the cause.
In my case, the issue is more academic than operational, so my concern is not great. Still, 'tis a problem that would be fun to resolve.
In the meantime, I'll keep mucking about and seeking a solution.
I also wonder if the age of my iMac (mid 2010) is an issue...
