Aye lol, might be worth checking if the pistons dust seals seen better days and allowed some dirt to get onto the piston then you could try a bit of red rubber grease and see if it gets any better, it may do a bit but i think you'l be requiring a caliper in the future, id rebuild it if i could as i'm a tight c**t haha
Various peugeots, citroens and other renaults use the same caliper so shop around for one if you decide to change it, just make sure the pistons the same size as it can vary!