I bought a pair from dealer yesterday, £151.60 each. The diesel ones are showing as 24mm balljoint part number ending in C and the later ones/petrol ones ending in G have a 21mm balljoint... I think your best bet is to go genuine, it's a critical part and i would not skimp on it by going for cheap parts ! Chap on forum (alski) had cheappo arms fitted to his allroad by a garage and the bushes were coming apart from the arms, look for the thread as it has a few pictures...