I agree with you, however I touched on that in #1. I don't know how successful lubing certain cables might be. If the cable can be separated from the sheath, and then both parts inspected, cleaned, lubed and reassembled, success would be high. I'm not sure how other MB cables are, but my 123 cable does not come out of the sheath. If the cable is binding, it's grinding and unless you can get the resulting abrasive 'metal paste' out, you'll continue to have problems. With the cost of the cable being low, I think if you are going to go to the trouble of removing it at all you should just replace it and be done with it for a long while, if not forever. Nonetheless, if lubing the speedo end of the cable has worked for you (and for others as I have noticed searching and reading several other related posts) then it should be included in this thread; there is no such thing as too much knowledge.
1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick