I just bought a used Pinarello bike that's in great shape. The only issue is that when I went to put the left peddle on, I can see that it has been cross threaded so my left peddle won't go on. I think the person I bought it from should have to pay for it but I'm trying to make it easy for him because I'm a nice guy like that.

I'm looking for just the left crank arm, but I can't seem to find one anywhere close or cheap. The crank set is an FC-R563/FC-R565. In my searching I'm finding that it might be cheaper just to buy a whole new crank like the FC-5750. All this is Greek to me so I'm hoping someone knowledgeable can guide me. Would buying the FC-5750 crank mean I need to change out my back wheel cogs as well or is it a strait replacement? Should I stick with my search for for a FC-R653 and where would I go to find one?

Any help will be much appreciated.