Ultimaker 2+ - Visible Layer Lines

[PrintPlace 0]

Hi, a while ago, one of our UM2+ (UM2 upgraded with Extrusion Upgrade Kit) started printing visible layer lines (refer picture "BeforeMaintenance" in attachment). The cause of the issue was not printfile-related, as the same file printed perfectly on one of our other UM2+. The printer in question was scheduled for maintenance, so we immediately performed thorough maintenance, i.e. we replaced the trapezoidal nut (the thread was cracked slightly in one spot), we stabilized the Z stage (alignment of bearings for smooth manual movement of the print bed), we reinstalled the XY linear shafts (making sure the pulleys are correctly positioned and the timing belts are tightened, both the timing belts of the motor and the axles) and realigned the print head axes (using the alignment tool). We printed new tests and although the results are much better, they are still not ideal (refer picture "AfterMaintenance" in attachment). From our tests, the visible layer lines do not show up on the same height, but are rather printed randomly. 

We were wondering if someone from the UM team or the UM community would be able to help us get to the bottom of this. We were considering to replace the pulleys and timing belts, but at the same time they haven't been exposed to that much wear - far less than some of our other printers - so we wanted to post the question here first 🙂 Thanks!