From people that say things, it sounds like the brakes only last a couple of seasons before seals wear out and your brakes start sucking air. udi rants about a plastic bit in the master cylinder and kidwoo talks about a leaking, no-replaceable piston seal, so the choice is yours as to why the brakes start sucking. I have a pair of XTs that are good but the first few initial squeezes always have that pump up. As for replacing them, I'd say you'd have a hard time finding a cheaper and better lever set than the SLX/zee levers for $24 from jenson that are always brought up. I wouldn't recommend the levers from magura but you might be able to score some sort of apparatus off of ebay. Formula makes mineral oil levers now, but it might be a challenge to get them and to make them work with the large piston surface area of your zee calipers. It might be wiser to think about a complete set of brakes, and move on to something that people hate the least.