My FSM (1980) says to use white lithium grease on the balls.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

For what it's worth....I just had one of these sockets fail and almost left me stranded. Swapped out with the cruise linkage to get home.

Called the dealer and they had a few in stock....The best part......$5 bucks for a brand new socket.