I just applied a couple of drops of 90W gear oil to the lubrication hole on the top of my "67 250S.

Result: A reduction in the panoply of noises coming from the engine. I can not really describe the noise it had been making; but there was less of it. I have owned the car for nearly 4 years now, and just now noticed this lubrication point.


References:

- Service Manual (BBB) from 1959:
See Job No. 0-9.
** A Lubrication Jobs" --
Item - Water pump, steering gear housing (standard);
Job - Check oil level, top up, if requ. (sic);
Plan E every 12,000 m - all [models]; and

** B Lubrication Chart

Also
- Chilton's 1970 Mercedes Benz Repair & Tune-Up Guide
** Page 18:
Lubricant Recommendations chart. References SAE 90 Gear/Lube from Lists 1 & 2 for "Water Pump".

It is interesting that neither the BBB nor Chilton's goes into any appreciable discussion about the water pump beyond these cited areas. Perhaps this is the reason that there is a lot of puzzlement about whether this is a bona fide procedure.

Happy motoring!

__________________
Currently enjoying:
1967 250S - all manual with 4-spd on floor-- my Nifty 250