You may be able to get away with just cleaning the front brake caliper. Remember that the only things to clean the square section o-rings and pistons are fairy liquid with water ( cold ) and/or brake fluid. Be careful not to lose the wee o-ring between the two caliper halves. You will need to take care that the square section o-rings are seated properly in the caliper before re-installing the pistons and be careful you put the pistons back in true to the caliper bore. GOOD LUCK.