The OE MB star items have some really really heavy black grease in them and a nylon cup in which the ball rotates.

I practiced a couple of zerk fittings in my old busted W124 ball joints and the problem is that the bottom cap is sheet metal and is very thin - meaning no threads catch unless you have a tapered zerk fitting. Once in I did proceed to pump it till it flushed.

What I did learn is that it will be pretty much placebo if you push some grease in the boot only.

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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)