First off, it may not even be the pump. You could have a hole in your drop line if it's galvanized, a split if it's black PE pipe, or a clogged intake. Seen all three things happen before.
Secondly, 12 years is a good run. Why even bother repairing the old one knowing that the motor etc. is already that old? If you're that determined, just buy a new wet end and re-use the motor. What kind of pricing (American dollars) are they giving you?