Yes, I came in to the office early, wrote down all the software that I needed to reinstall, saved the important stuff on 2 other drives and took the plunge!
Erased Macintosh HD and reinstalled OX 10.5, software updated, installed M100 12.7.1, Kona 5.1.1, FSC, AE, PS, Toast, Word, PPT and the other favourite software apps, ensured updates were downloaded & installed, Disk utilitied from time to time and SO FAR SO GOOD WITH MEDIA 100!!!!!! (and everything else for that matter)
Mind you, all of my new M100 projects have been imports of existing files provided by my clients, so the REAL test of capturing off tape has yet to be conducted. I had to put clients' jobs back to fix my problem of course, so now they come first.
I have noticed a few extras such as additional fonts, auto update monitor now works from the M100 titler. Never worked for so long! Additional codecs was an interesting observation, not that I use more than ProRez422HQ, but they are there. Subtle but nice improvements.
But it took ALL DAY to do but who cares if it fixes my problem!!! I will post the final installment to this thread once I capture the same clips in the same project that caused me such a problem.
Thanks again Floh for persisting with ideas that confirmed what I was thinking I should have done in the first place but was to afraid to do!
It may not be a physically challenging task to wipe your HD with the OS & apps & reload all over again, but it sure is a scary thought. Once you start, it's not too bad. It even felt refreshing seeing a HD with over 1 million files (Disk utility) reloaded with about 350,000 files now. Nice and clean & hopefully no hardware problem after all!
Now do yourself a favor, install a second internal HD, and use Carbon Copy Cloner from time to time to clone your startup drive. In case something goes wrong again you simply can start up from the second HD and you should be up and running.
Before I took the plunge, I did a test install on another HD and it worked, so I did what I did to the Mac HD. Seeing the test 700Gb HD is still in the computer, I will do EXACTLY what you have suggested.