I had a problem with the push fit type bearing holders in the stock Reprappro Huxley breaking every time (3 times) I tried to insert them. In truth the problem most likley lies in one of the following things
1) me being clumsy
2) not properly deburing the inside face
3) More than likely my slicing settings where no correct ( I have since found setting a fixed extrusion width ratio in Slic3r to have improved its output no end)
But for all you other clumsy fellows I went down the route of modifying the original parts to be shorter and accommodate zip ties on the holders. Use a small dab of super glue and zip tie the LM6UU down. I found the X carriage to be just as easily broken but a dab of super glue will be more than enough on this part.
Please note I modified the STEP models from GITHUB using 123d but found the floating bearing holder to be a slightly different shape (older?) to the stl one in the zip file on thingyverse. This shouldent make to much difference though as all the hole centres are the same