I've got the same problem on my XR4x4 and I'm 99.9% sure it's the front hubs that are bent/distorted, it is common problem on the XR but I don't know if the Cossie suffers from the same thing, clamp the disc to the hub with some wheel nuts and give them a spin with a piece of wire clamped or bolted on to use as a pointer on the outer edge of the disc, if they run out of true with new discs then the hubs are fooked.

Mark