is your workshop heated, if not you might have to, I find that temprature changes in the room change the dewpoint and any moisture in the air will condense out on any large metal objects, I used to be bothered by this problem and installed a couple of small tube style heaters near to my machine tools and this cured the problem, a small increase in the 'leccy bill, but piece of mind on the tool condition, an added bonus is that once the machine tools reach and maintain a constant temp, theres no variation on there acuracy