I'm afraid it might come down to taking the pots out and cleaning plus removing the seals and cleaning those and the groves in the caliper (where seals sit). Its just one of those jobs that need doing ever so often. But before that have you cleaned and greased (red rubber grease) the sliding pins on both calipers? This is the first thing to check when the brakes bind. Make sure you don't have too much grease in the holes as this will screw with the caliper. I clean everything, grease the pins and put some grease in holes then reassemble caliper. Then push the two part of the caliper together. If there is too much grease the rubber bellows with bulge so I use a small screwdriver to lift one side so the excess comes out. One other thing to check is the alignment of the wheel. Another is the master cylinder sticking.

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