The y-axis rail guide of our MakerBot broke. Since we have two printers, we were able to print a replacement part. So there it is. Have fun.

Video: https://www.youtube.com/watch?v=BJH9YAaovrM

You may have to print a few versions until you get a result that perfectly matches your makerbot. If not, you need:

1x mbr4.stl
1x mbr4pt2.stl
1x mbr5pt2.stl

Depending on the side you may have to mirror some parts.

You also have to dismount the gears and remount-it in the part. This is a little bit tricky, but a lot more stable than the default MakerBot part could be at all.