Rotax like motorcycles share the same oil in the engine and gearbox. Automotive engines do not. Automotive oil does not have the same additives that motorcycle oil has in them. Using automotive oil in the Rotax for extended periods will cause extra wear in the gearbox. Automotive oils cannot handle the close tolerance shear forces in a gearbox. Using an automotive oil in this engine will cost you in advertised oil weight properties. As an example if you use an automotive 10-40W oil as soon as you use it in this engine it will drop to a 10-30W. Shear forces and tolerances are too great. Automotive oils don't have ZDDP which is a sacrificial zinc phosphate additive to help coat metal parts. ZDDP will foul automotive catalytic converters.
Aeroshell Sport Plus 4 is a semi synthetic 10-40W which is suitable for most places in the world. Aeroshell Sport Plus 4 is only MFG'd in the U.K. and no place else.
Aeroshell Sport Plus 4 was designed with just the Rotax in mind. The a few years later shell teamed up with a few flight schools that were putting high time hours and their Rotax engines. So they embarked on a new study to determine the properties of their oil versus wear. After the study with thousands of hours Shell mad changes to the base stock and the additive package to better suit the rotax engine. The new red bottled Aeroshell Sport Plus 4 is the new formula.
There are a few other oils that can be considered safe to use and they are motorcycle oils.
If you use 91 oct auto fuel you can use either a full synthetic or a semi synthetic. If you use 100LL most of the time then you must use semi synthetic because a full synthetic will not suspend the lead in the oil and it falls out everywhere in the engine.
Aeroshell Sport Plus 4 just makes it an easy solution to use for either fuel and you know the formula won't change and it was made specifically with your engine in mind.
One place to buy it is: