With each post I, again, verify without prejudice. Chip is DS1337, "Special" registers report valid (functioning) values before being written, and verify valid values after first write (as described in RTFM). I did not notice low capacitor values, rather stuck a crystal in the appropriate holes without consideration for any value but frequency, yet it has worked without glitch for several days until after I thought I loaded "perfect" version of code.

I will see what I can do with that... though ordering crystals is as time consuming as ordering chips and, I still don't know if/ why it worked so well and stopped so suddenly.