Marting, the link on your thread had some interesting info that may further the complexity of choosing an oil.
"Extreme Pressure (EP) Gear Oils
EP mineral gear oils are used more extensively in worm gears. Under conditions of high pressure and temperature, the EP (antiscuff) additive reacts with the metal surface to form a soft, slippery chemical layer which prevents severe wear and welding. Previously, there was a concern that sulfur-phosphorous EP additives would react with the bronze gear. However, new EP additive technology used by most of the major lubricant suppliers has reduced the corrosive attack by utilizing nonactive sulfur. EP lubricants work particularly well when shock loading occurs. EP gear oils also protect steel gears better than compounded gear oils.
Typical recommendations are for both AGMA 7 and 8 viscosity grades. Like compounded gear oils, EP gear oils limit operating temperatures to under 180°F (82°C).
Typical commercial oils: Shell Omala, Texaco Meropa, Exxon Spartan EP, Mobilgear 634 and 636, and Chevron EP Gear Oil.
Synthetic Worm Gear Oils
Two major types of synthetic gear oils have been used successfully in challenging conditions with worm gears: polyalphaolefins and polyalkelene glycols.
Polyalphaolefins (PAOs) are the most common type of synthetic lubricant. They have good high and low temperature properties and are compatible with most mineral oils. Unlike some synthetics, PAOs don’t attack paints or seals. Most formulations contain a small amount of organic ester or antiwear mineral that improves boundary lubrication conditions. Products that contain EP additives are also available. There are no major disadvantages, other than cost, when using PAOs as worm gear lubricants.
Typical commercial oils: Chevron Tegra, Texaco Pinnacle, Exxon Teresstic SHP, Mobil SHC, Shell Hyperia and Royal Purple Synergy.
Polyalkylene glycols (PAGs) are excellent for worm gear applications. They possess superior lubricity properties and have good low and high temperature properties. The Viscosity Index of PAGs is higher than most synthetics, approaching 280. Therefore, a lower initial viscosity grade can be used minimizing internal friction resulting in improved worm gear efficiency. Most PAGs contain antiwear properties but there are no formulations with EP additives.
Besides cost, a major disadvantage of polyalkylene glycols is their incompatibility with other fluids. They also attack paints, seals and polycarbonate sight glasses."
So, this clearly states makes the case for synthetics. And it also makes me wonder if the EP additives in auto gear oils are actually in fact a deactivated Sulfur that won't attack the yellow metal. I wish the article dealt with consumer oils rather than industrial oils.
