Rework of the stock MK3 R3 X idler which allows +/- 1mm of rod length adjustment. The final length is locked in place using two M3x8 screws.
Only valuable for custom builds, such as the full bear upgrade. This is unlikely to be useful for the plain MK3 or the bear half-upgrade.
I noticed the Z screws were simultaneously flexing in opposing directions when going full up or down, a sign of rod-length mismatch for your assembly. Note: if they displace in random directions then rod-length is not an issue (release tension from the POM nuts, if any, then check again).
If the screws don't touch the hole in the Z tops you're still fine. But now that you noticed your OCD will kick-in and deep down you know you'll have to fix it: we're not here for "good enough".
Print at 0.2mm with 0.1 for the first layer (this improves rod center alignment) or at 0.3mm through-out. Use 3 perimeters at 30% grid infill. Ram the holes with a 8mm drill. Check and clean any debris, especially in the pockets.
Insert the M3x8 screws, which will self-tap the holes. Keep moving the screws until they don't squeak anymore: you'll need some feel while tightening later.
Insert the rods and push them fully. The assembly should be 1mm shorter than stock length. Tighten the screws until you feel some tension due to the rods touching. Insert the assembly into the Z screws/rods. Insert the Z tops to align the POM nuts and tighten them, but do not tighten the Z tops yet. Move the carriage fully down and watch the direction of the Z screws: if they go inwards rotate 1/4 turn of both screws and repeat by moving the carriage up and down again.
Go slowly: if the screws start to go outwards the rods are too long. Due to the fit of the X rods it's not possible to easily shorten the carriage. Remove the assembly and push the rods fully back in before trying again.