If its a known problem with pumps of a particular year then I can understand where your coming from but if its simply from another car it could fail after 5 miles or 50,000 miles and at £50 I'd take that risk either way over £440, you could get one that fails after 2000 miles and then get another one that lasts for the rest of the time you keep the car, you'd still have paid out alot less than £440.
Or you could just drive without the pump and save on gym subscriptions