A question that comes up now and then.
In my original Handbook (second issue April 1934) it is stated to use the same oil as for engine in the sliding pillars, like Veedol Medium 3. On the first page of my handbook, a additional page has been stuck on, which states the usage of lubricants of several Lancia car models. I think, that No. 3 oil would be about SAE 30 grade.
In my car I use SAE 30 single grade oil for the engine and the Sliding Pillars. The differences would be the operating temperatures, therefore different viscosity. No problem in all the years.
Karl