Given the high price and "lifetime" claim for WS atf I assumed it was synthetic. I bought some for a change and found a MSDS in the bottom of the box. The salient point: "mineral oil concentration by weight- 80-90%" To me this means dino oil. Viscosity is given as 23cSt@40c and 5.45cSt@100c. Make that really thin dino oil. The only synthetic I find in the marketplace that is recommended by it's maker for this application is Red Line D6 with a viscosity of 30.7cSt@40c and 6.4cSt@100c. Does anyone know of any other suitable synthetics?