I had the other driveshaft out when I swapped the box, it seemed fine to me. The one I think is faulty looked fine too.

The car will drive for a little bit before it locks up so I guess it's hard to tell. There is no obvious signs anything was wong with either, but I suppose it's hard to tell unless when they are not under load.

The biggest pain in the arse is I had a pair of driveshafts and grinded through them when removing the gearbox from my spares car.