I think mantra must be right - but not a good clue is it? First a mantra isn't really a text - just a phrase. Tantra would be better, but doesn't follow from the cryptic part of the clue - staff (man) facility turned over (art reversed). But again an art is not a facility - a facility is something that comes easily, art requires a combination of talent, training and effort.
I've also been stuck on this one - cheers :) if mantra is right then I agree it's not the most satisfying clue, but there's a pleasing efficiency in the elision of 'facility turned over' and 'turned over sacred text', which after all roughly defines the specific nature of a mantra among other tenets!