I’ll say that the form Roller gear is slipping off the track. I notice it’s when the vibrating roller shifts to the near side mostly. The only thing I have noticed is the first form Roller L shaped hinge is loose turning and has to be checked and turned back. There doesn’t seem to be anything to tighten it. I tried lowering the geared form Roller but had no effect.
I’m sure it’s something simple, but it’s not coming to me.
Here is a short video. I have a slightly longer one if that would be helpful.
Here are the pictures I mentioned in my last comment.
UPDATE: I had the chattering problem again twice in the print session. Although we had done maintenance which consisted of : 1. The end screws did not have set screws in them. 2. But loosening the set screw on the core (it was hard! Used a soldering iron to warm up the metal and vise grips to turn the Allen wrenches) allowed the end screw to come off. 3. The woodruff key was present. 4.-5. Everything got cleaned and oiled. The threads were in good condition. 6. The bearing assembly was cleaned. 7. After D went back inside I located a tool for taking the lock screw off the bearing assembly! ( Because he got to do all the fun stuff)
8. I used this to switch out front form roller one with the loose L-bracket, scavenged a lock screw from another and installed it.
I am sharing another video here. What I am questioning is whether the gear is supposed to shift back and forth like this, and would it be enough to send the roller down the track while skipping the the correct teeth.