all mine jammed and seized, I learnt that when the cassette started to wobble you only had a couple of miles left in it, before you were going to have to walk.
From what I was told by Merlin (and Shimano tech support) the freehub for the M775 is unique to this wheel (and 1 revision on the XTR wheels, but they are even harder to track down). So you need to specially order it.
Give madison a call, and they should be able to confirm all this, and let you know how much a new one is, and how long you will be waiting for it.
Its a shame, as those wheels are strong, light, ust and not that pricey. However reliable they aren't.