Agree with Readymedic, Royal Purple makes very good lubricants, and their 100% synthetic ATF should work great in a Diamond Drive.
MI1M600EFI's home brew lube makes sense (50/50 synthetic Supertec 75W90 and Valvoline synthetic Max Life ATF) in terms of viscosity, 20 wt overall. I think that's the same as the Amsoil Synthetic Snowmobile Gear Lube I use. Our Diamond Drives spin so fast and operate in the cold, so thin is important. Non-foaming is also important. Mixing synthetic oils is normally not a problem, and as proven by MI1M600EFI's experience. However some older type synthetics are not compatible with modern / best PAO synthetics, and chemical additive packages occasionally can conflict. Don't see any advantage to using 50% Dino oil in the Supertec, other than to save cost.
Agree with Coldfinger, we shouldn't use hypoid gear lubes with sulfur / phosphorous extreme pressure EP additives for sliding (hypoid) differential gears. Some of those additives can damage brass / bronze. GL-5 has more EP as compared to GL-4.
Overall, IMO thin Synthetic lube is very important in a Diamond Drive due to: 1) the huge temperature range from cold starts to long, hard pulls, 2) very high-rpm Diamond Drive operation, 3) PAO synthetics are less-affected (less damaged) by water contamination, as compared to any other types of oil, and 4) Synthetics have 10 times the film strength of Dino oils, as needed for the heavily-loaded 3203 bearing.
If you continue to have Diamond Drive problems, reducing the thrust load on the 3203 bearing is also important. The tunnel / track driveshaft mis-match many of us suffered is fixable. And any bearing / lube combination works better / lasts longer with less load.
Good luck, happy holidays & safe riding!
