Can the actual drive cable be pulled out from the cable housing on the Mercedes? On some of my old English cars, I would just pull out the inner cable from the trans end, wipe it off and grease it with some lightweight grease. I think I used white lithium grease, iirc. Then it's just a matter of feeding it back into the housing and twisting it till it engages the speedo. I did this every couple of years and I never had one break or wear out.

Gary