Schaeffer's 75w140 full synthetic. Was new in 2012 and apart for inspection last winter and nothing outside of some normal and very minimal wear.
Should be quite a few good gear lubes out there. None of which should need or require any additives, should already be in the formulation.
On the TD sheets you can find the viscosity index, extreme pressure, anti wear properties and all the standardized testing that the product should have went through.
The good oils aren't afraid to share their results.
