Yes, but ...
Originally Posted by archphoto
a) Grease needs to be replaced as part of normal servicing, not usually because of sand or grit but because it hardens and dries out with time. The service interval could be anything from once every 5 years for a professionally-used camera to once every 40 to 50 years for a camera subject to light amateur use.
b) Independent repairmen (at least the ones I use) do use the right materials! The difference in cost between the cheapest and most expensive grease in the quantity needed for one lens is TINY!
If you buy a lens on e-bay or elsewhere, you will of course ask the seller whether the diaphragm is working smoothly. If it is, no problem - if it isn't you either factor it the cost of servicing or find another lens. The whole point I am making is that 1950s Leitz lenses can be perfectly usable and offer picture-making possiblities that other lenses don't!