The locks can be repaired but you will need some special tools to do it right and these outweigh the price of a new lock.
First remove the lock and then the chrome cap this can be carefully prised off with a small flat blade screwdriver "Watch your pinkies" :) or a proper cap removal pliers, then disassemble the lock and repair as required.
To put back together you can with a small hammer end crimp the cap back on or use the proper cap fitter from Citroen or Peugeot again costly if you want to buy.
Things that go wrong with these locks with a guide to what i think is the more likely to be wrong 5 stars always 1 star rare.
Blockage at the key tip in lock **** Can be flushed?
Worn pins ***** Need pins replacing
Key guide broken inside *** Needs new lock
Broken key left inside * Some people hmmm
Cap failure * Realign
Complete breakdown inside **** Needs new lock
Key worn **** Get a new one cut
Hope this helps anything else add it yerself I'm not god you know :)
Wittybebop, April 2007
