You can buy those ball cages from some CV axle rebuild outlets. I think rockford and GKN driveline shops or any decent CV rebuild business can get you those cages. The guys running the older SAABs are on that sort of rebuild level now as parts are NLA for those cars.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)