I cannot really see how it can be a sticky caliper. Sticky caliper normally overheats the disc and warps it, you then get wobbles which won't go away until you replace the disc.
Maybe a sticky piston (dual piston brakes) which is putting uneven pressure on the disc?
I still think it is rust on the surface - different thickness under the pads to the rest of the disc which causes the wobble. The rust would be worn off very quickly though.