Yeah, a brembro pr4 is used alot., especially by zee germanz, theres a post about this, where the caliper options are talked about at length
Its used on lots of bikes, and therefore easy and not that pricey to get hold of (looks to be £50ish
http://www.ebay.co.uk/sch/i.html?_nkw=r ... &_from=R40)
But you need an adaptor made up. and some people use the xt600x disc as thats slightly offset (helps with clearance issues with caliper/spokes)
If my caliper started going funny I'd do this or the Tokio caliper and adaptor as already mentioned.