Print bed rises and lowers on left side when moving

On my Mini 1 the print bed rises and lowers as it moves back and forth during printing. It is not much but visible if you watch closely. I thought it may have been a bent guide rail so I replaced them but still have the problem. This up and down motion is only on the left side of the print bed and it seems to be at the same place every time. The wire chain does not seem to be causing the problem either.

See the attached videos.

Any ideas of what else I can look at?
20190205_212843[1].mp4 (13 MB)
20190205_212802[1].mp4 (12.2 MB)

The bed bearings are worn and need replacing. I bet if you look at the side of a print that faced the left you would see two indents on the print evenly spaced.

I am having the same issue on my Mini 1 and support said I should replace the bed bushings. they are on their way, but I am wondering how to replace them? they seem pretty tight in the bed rails. Also any thoughts about replacing the Igus bushings with linear bearings and hardened steel shafts? Thanks!

Hardened rods and steel bearings tend to be noisier and can introduce surface artifacts in the prints.

The best cost-effective improvement to make on the Mini bearings is to replace the RJM-01-08 bearings with RJMP-01-08. The RJM ID tolerance is +0.025 +0.061 mm. The RJMP tolerance is +0.000 +0.030 mm resulting in a much better fit on the smooth rod.

Here are a couple of videos comparing RJM to RJMP. RJM is first in both videos.

Where does one obtain RJMP bearings?

Sometimes you can find them on Amazon or ebay. Just be careful they are genuine and actually RJMP. I have seen some listed as RJMP that were RJM. You can also buy direct from IGUS.

My issue turned out to be a bent frame, probably from shipping after I bought it on eBay. After I replaced the bushings, IGUS is the best place to buy them, and the rods, I took out 5 links from the cable chain going to the bed and the problem is solved. I noticed the dent in the bottom of the frame while I was putting the bed back together.