Our great MakerBot Replicator 2X's Y-axis rail-guide broke...so we built a STRONGER replacement. Since we have two printers, we were able to print a replacement part.
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.
1 screws Ø3mm - lenght 20/25mm
5 bolts for the screws