yes there is am O-ring inside the caliper can be change and align back the caliper piston..
while at the brake system better check your master brake pump, ur rear brake pump(drums)/ rear disc service the caliper n align back the piston.
if wanna better brake change to a bigger servo
used afi, trestor, don 3 star, stock proton pads all used on a cross drilled rotor n got a very effective brake...

hope tis helps ya..