Hi Geoff, used to live in sunny sudders, If you are considering microswitches, most machines I have worked on have used a quality made switch say Honeywell, with at least a 1mill cycle life expectancy. Also belive it or not apart from bad setting the single cause of premature failure in these switches is the tendancy to fully compress them when they are unpacked. I have admonished many an apprentice for clicking a new switch in the hand. also limit and ot switches should be a roller type working from a cam with an actuation ramp length of at least 4 times the dia of the switch roller.
Guide protectors are available but expensive, the integral wipers on bearings cannot be relied upon permanently especially when passing the screw caps of the rails. One system I have used is to assert a low air pressure to each bearing therefore blowing out contamination, but these were relatively low traverse speeds and the particulate was brass, all the best Tony