Canon 17-40mm lens, focus ring binding, missing shims?

Lens repair gurus - would appreciate your help!

Just repaired a 17-40mm with a broken front barrel (filter threads broken) which also had a problem with a stiff focus ring. I was hoping replacing the front barrel would remedy the focus ring problem, but it didn’t and I ended up replacing the middle barrel as well, but the focus ring is still very hard to turn. (A problem from before I started the repair.

Its not binding in any one specific spot of the rotation, and it isn't bent (checked with caliper). It rotates fine before I tighten down the middle barrel, but once its tightened down it starts to bind and become really hard to turn. The autofocus works perfectly fine as do all the other functions of the lens.

Could this lens have been disassembled before and had some kind of spacer left out? Or is there some trick or reassembly procedure i'm supposed to be following?

Again, thanks for any help!