Buy another off ebay, they are cheap. If that doesn't work then use the freehub from a DX or LX level as a replacement. I have seen a few NOS XT replacements too but it is cheaper to just buy whole hubs.
Most older freehub bodies are interchangeable. As far as I can see there is no difference between them anyway. STX still seem to be readily available as spares and definitely fit.
Also, don't let GT85 or similar anywhere near the rear hub - it washes the grease out. Since I learned this I have had no more freehub failures.
Cheers for the help everyone,think i'll start with looking through all the spare wheels and check those shimano freehubs. The only reason i'm bothered is there the black xt hubs i've got on my 1990 explosif and finding a replacement complete hub would be a nightmare