@Muzzer. Thanks, there isn't a lot of room on either side for the telescopic ones, but I'll look and investigate if I can fit them in. My lathe has the same thing over its leadscrew, and I must admit I don't love the noise they make (how yours for sound levels?). Still seems like a simple solution, but I'd still feel more comfortable if the nut's seals were a bit better as well, and maybe had some kind of rubber sweeper... I don't know.

@Voicecoil. Thanks for that, I had a nose around the TBI website you liked to, I guess I'll ask Fred for a quote too. Did you go with his ballscrews in the end? I'm guessing not the TBI ones?