When you say knackered how do you mean knackered ?
My friends xr3i one was stuck solid and wouldnt budge abit of wd40 on it left it to soak for abit then just kept working the lock spraying abit more wd40 every now and again he had loads of gunk come out of his as we worked the lock and it free'd it up loads.
just an idea for you to try before you try a new lock
mark.