As for lubing the speedometer, all you can lube is the slot that the cable plugs into. I'd use a good gear oil, like mobile syn. but any heavyweight oil would work.

As for internal lubing, I don't think that's a good idea. I have never taken a MB speedo apart but most mechanical speedometer and tachometers that I've seen use a magnetic or electromagnetic coupling between the cable and the reading needle. Some connect the cable to a magnet, that when spinning by a coil of wires will induce a current in that wire which is proportional to the magnets rotational speed. A second coil connected to this will induce a magnetic field that will draw on the speedometer's needle. Not much to oil here...

I know that some shops particularly fix and repair speedometers and tachometers.

ATLD

I have a reference to an excellent shop but $70.00 seems a bit excessive at the moment...
Thanks for the insight.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

my 87 300d broke 3 speedo cablles in one week as well,i now have a piece of the cable stuck in the housing at the trans,it will not come out and i believe the gear may be stripped in there,anyone had this happen?