if your piston dust cover is split letting in dirt etc, may be starting to seize up,pull back cover and check there is no rust or pitting on the piston and check pads are nice and free in the bridge,if not get some copaslip and lube them up and make sure everything is nice and free,if no better maybe worthwhile going to a scrappy for a good 2nd hand caliper
wickham, June 2010