I have had problems from the start of slag and other undesirable materials getting into the gear rack. I perssonaly believe it should never have been designed to face up but I can't really change that so I opted to fix that with comppressed air jets. Using my lathe and mill I built three jet modules, each with a jet to blow air on each side of the spur gears as seen below:
I fabricated 2 X-axis modules as I have modified my TM2 4x4 to run two X-axis motors and then used the torchmate to cut out two brackets to mount them to the machine as seen below.
I made a third and used my lathe to make some pins and welded them to the module and bolted them to the Z-axix motor plate. I then ran some hoses and voila I have since had a problem with anything. In fact the little 1/8 nozzles (made from grease nipples with the ball removed) blow so much air pressure that anything 6 inches away is gone so it really is great.