So the problem S3 was down around 430GH/s this morning and I decided to go over its probably reworked board, the board that had grossly over-tightened screws, but would try frequency change first. 

It had been down to 430 so I tried changing the frequency to check out its effect on hashrate.  In /etc/config/asic-freq I changed to f=225, rebooted and restarted cgminer to get a fresh time duration.  I gave it some time but it came up very slowly only to 420 or so.  And it was a cool morning!  All the other machines were hashing perfectly.  So, I tried again, this time with f=212.5 but again it came up slow and only to 417GH/s.  So, I ripped it apart again.

I was going to concentrate on its ASICs at the hot end of the reworked board, but ended up getting distracted.  What distracted me was that the board had marking in black ink at the far right under the top ASIC (on this board that would be near the intake fan).  Might have been Chinese or a code of some kind.  So, I cleaned that ACIC and the one under it with a spray of automobile brake cleaner such that all thermal paste was removed.  Must be careful with the stuff as it will mar many plastics.  I sprayed those ASICs cleaning around the pins, reapplied thermal compound to both sides of the blade and reassembled.  The brake cleaner removed the notation marks on that blade.  When I reassembled, for a change, I put the bad board on the right side facing the RJ45 connector.

I started it up then ran to the store and back.  Right now the 'difficult' S3, at a frequency of 218.75, after 1hr 20min, has an average hashrate of 443.74GH/s.  The temps are both 40° with fan speeds of 2040/1800.  Time will tell.