Ok so here is my machine setup:

ender 3 modified

y axis linear rail setup
silent board
microswiss direct drive and all metal hot end
th3d firmware (latest)
bltouch
cura slicer (latest)

Here is my problem: Im printing cylinders and my inner and outer walls (shells) are not printing concentrically. any ideas on what could be causing this issue? Full disclosure i bought this machine used so i do not know what happened before i got it. my prints are still coming out... but my inner and outer wall thicknesses are not consistent. and the entire part could be more of an oval... hard to know.

things i plan to check (or i have checked) after this latest print.
1. check the machine to make the x and y axis are square to each other
2. re check belt tension (looks pretty good)
3. model is good and the preview looks good in cura
4. create a cylinder that i can check with a cylindrical gauge
4. ?????

there is some "stiction" in the linear rail blocks but its not awful. nothing that i would think is causing repeatable non concentric walls. i would expect the stiction to cause random discontinuities in the print surface.

any help would be very appreciated.