Got to say I was thinking along the same lines as James, until I read the other thread & realised by Stephen talking about an 18 F3 crank that perhaps it wasnt a 21 we were talking about.
Even if it was a 21 crank, I`d probably get a new crank & have it trued for the sake of £50 odd quid more.
The way couriers chuck parcels around at the depots I`ve been to, would make me doubt that a crank would be in the same state it left the place it was sent from.
Just my point of view, I`ve also got another crank I got spare with my road bike. This has a duff gen side main. I will probably send it to you Andy, when it`s time. As this will probably be used in a race bike, & I`ll hopefully be able to collect it instead of using post/couriers.