So, everything has been going swimmingly with my BB build (well, apart from having far too little time to work on it...) and I'm in the midst of mounting the extruders to the print head, but I've hit a snag. On step 21.5, mounting the IR sensor, I can't get it to screw up tightly at all. One of the screw holes in the carriage is noticeably looser than the other, the M3 x 20 screw just drops straight in, bottoms out and cannot be tightened at all. The other side seems to be OK but with only one side attached the sensor flaps around no matter how much I tighten up the one good screw. I could tap the hole a little bigger for an M4 screw but the bracket arms seem a bit too thin to hold the cap of an M4 screw, or maybe use a longer M4 with a washer flat against the top instead of in the recess, but I'm not sure if the protruding screw head might then snag against anything elsewhere and cause me problems. Anyone else hit a similar problem or have any other ideas? I could potentially glue the screw in but I'm not sure if I'll need to adjust the IR sensor height later.