I've been looking back at 2c gearbox recommendations - and there is no real good answer here. Check that. All good suggestions....but just many different good options!
Since gear oil 75-90 is roughly the same viscosity as 10-40 motor oil, I went with 10w-40 Mobil 1 Synthetic 4T motorcycle oil. Bottle says for engine/trans/clutch usage.
From the Amsoil site:
Gear Oil and Motor Oil Are Not the Same. Gear oil differs from motor oil. While many motorists may assume SAE 90 gear oil is thicker than SAE 40 or 50 motor oil, they are actually the same viscosity; the difference is in the additives.
Just "looks" heavier......EP (I assume Extreme Pressure") lubricants have a lot of sulfur in them as well...giving that wonderful smell!
Castrol has a 75W80 gear oil for motorcycles that I've been using on my 2C for years. I did try engine
oil but changed back when I experienced some clutch slippage. Having said that, lots of things cause clutch