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Over the years the rubber inside the hoses have a tendancy to swell, and will completely close keeping pressure applied to the caliper.
Pull the brake line loose from the caliper and see if the rotor is still in a bind. If that is the problem, you will want to replace both sides, because the other will soon have the same problem.
If that doesn't fix it, you might want to see if the piston is stuck in the caliper.