Upon further investigation, it appears that the breech bolt tooth is worn out. It strikes the bolt assembly at a different angle depending on the position of the c.d.l.
I also have had problems with carrier spring plunger popping out.
Your patient help led me to the conclusion about the bolt tooth. I called Brownell's today, talked to a tech. and went ahead and ordered a trigger assembly.
Ten years of heavy shooting should wear things out. I'll give an update later. Thanks. V