(straight) Rear leadscew is wobbling

Hi! here’s the situation: I got a used V3.1 that had a badly bent REAR leadscrew, so I bought and installed the following replacements from the official RR store:

  • new leadscrew (looked 100% straight, rolling it on a table showed no imperfections)
  • new coupler
  • new bearing to connect motor and coupler
  • reprinted the pillow part on which the coupler sits (bc the previous one didn’t let the bearing sit flush inside)
After replacing all of the above, the situation got better BUT the leadscrew still bends a bit more compared to the other two. (see the two videos, it looks wobbly AND kind of erratic, sometimes it abruptly changes its position. I removed the upper stabilizer thing just for the videos.)

Could the motor be the culprit?

Is this normal for the rear leadscrew specifically?

Am I forgetting something?
Solution
@TheTik @VisualTech48 @IronBrain Thank you all so much for the answers!

I finally had some time to do some more checks and it looks like the motor shaft is seriously wobbling.

Since I just made an order on the RR website and wouldn't like to pay 14$ of shipping for a 14$ motor, could I ask:
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