Pulling to left under braking
My 159 has been pulling to the left under braking since I bought it. The dealer has agreed to pay for it to be fixed (but is over 150 miles away, so I can't easily take it back to them). They've a contract with a 'well known chain of autocentres!' and want me to use them. I took the car in to them and they performed some diagnosis. They spotted that the left hand front brake disc is heavily worn, as are the pads, much more than the right hand side (I've checked and they're right). They also found that the left caliper is braking much more than the right, but the right is 'within specification'.
So, they suggest replacement of front discs and pads (I agree), but also replacement of the front LEFT caliper - as they say it's 'sticking'. This doesn't appear logical to me. If the front left caliper was sticking, wouldn't it be less efficient and the car would pull to the right? How can a stuck brake caliper be more effective.
Is my logic flawed, or am I being given duff advice?
P.S. The car doesn't pull or drift at all when not under braking.