If you have a V1 drive with a broken cable or chain , you will now need to  purchase a V1 drums/cables update kit to  GT (covers V2) which will

give you new drums , idler pulley ,  idler cable , and miragedrive chains and nuts . Part number 81171002

 UPDATE KIT-V1 DRUMS/CABLES TO GT

 2 x GT Drums

2 x V2 Miragedrive chains

Gt Idler Pulley and V2 idler cable & nuts to suit