Hi,
I actually got in touch with B&W a couple of days ago, spoke to a very nice chap. I explained I had a ding in the dome and he recommended a replacement at a cost of just shy of £25 inc. P&P and comprehensive layman-termed instructions. Pretty darn reasonable, acsh. I'll ca'canny* just now, and invest at a later date, as I'm not sure there's any audible reason to replace it just now. Oh, and he recommended just to replace the one, and just leave it to run in for a few hours, and it'd soon match the other.
Ta for all the info, everybody! (In the voice of Dr. Nick from "The Simpsons")
*Ca'Canny - Auld Scots: To make a wise decision. Often synonymous with "Hold your horses."