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movement between the ball and the ring of the rod end...
So if I understand you correctly it sounds like one of your rod end bearings is failing.
I have been watching this thread for a couple of days now, I didn't think it was the rods, but now I do.
I think you are on the right track. The hard part is going to be trying to find the correct length. I think most folks buy them too long and cut them to size, then epoxy the rod ends into the carbon fiber tubes using a jig, so they are all exactly the same length.
Or if you can find one rod end bearing to replace the bad one I think that would work also.
I have been using my carriages and effector and I am right on the edge of publishing another effector, a semi universal one.
Also I got rid of the trigorilla board years ago and I went with an MKS running smoothiware. OMG what a difference! It is so easy to upload a new configuration file, I got this printer totally dialed in. It is printing the best it ever has.
I don't mean to hijack your thread but here is a link to my carriages. They are belt tensioners also.
I hope this helps a little.
Oh and by the way, the rod end mounting points on my carriages and effectors are 52mm's wide, so you don't need the copper spacers anymore. One less thing to worry about.

Anycubic Kossel Linear Plus carriage tensioner