magura julie's... there is something not *quite* right about them, i think the disk *may* be warped, so will have to get that replaced, it doensn't drop down cleanly onto the forks either, and i think it has something to do with the non standard manitou fork mount... gonna give it the spring clean/oil re-allign next weekend and see if there is anything definately wrong.
It is probably the alignment of the Caliper and/or the disk mount. The manitous need a disk mount bracket to fit standard fit discs adding an extra degree of alignment I would slacken the bolts for the caliper and the disk mount, apply the brake to centre the disc (the disc should move to the correct position). Then partially tighten the fork disc mount adaptor and the caliper bolts. Release the disc and tighten fully. The disc should then sit in the correct position in the caliper.
This is what I did with my discs and manitous (not Maguras though). Also, you can put disc spacer washers bwteen the caliper to move it slightly to centre the disc.