Michael, a couple of years ago Rotax apparently entered into an exclusive agreement with Shell Oil.
Before this Rotax had a fairly extensive list of recommended motorcycle oils.
Be aware that, while best for lubrication, a full synthetic oil does a lousy job of keeping lead in suspension, and that Rotax engines are designed to use unleaded fuel. If you have to use 100LL (which contains about 18 times as much lead as the old 'regular leaded auto gas') you should use either a mineral motorcycle oil or a semi-synthetic motorcycle-type oil. Motorcycle oil contains additives which help withstand the high teeth contact pressures within gearboxes. Aerosport Plus 4 is basically a semi-sythetic motorcycle oil. (It is also made only in the UK, which may be one of the reasons for it being sometimes out of stock).
If using 100LL more than 50% of the time, change oil and filter every 25 hours.
If using 100LL less than 50% of the time, change oil every 50 hours.
If using unleaded mogas and a full synthetic oil (like Mobil 1 Racing 10W-40) you can go up to 100 hours, or once per year.
In my aircraft I use mogas and Mobil 1 Racing 10W-40 in the winter and Mobil 1 V Twin 20W-50 in the summer. I can buy Mobil 1 motorcycle oil at the local Walmart. It costs about the same as the Aerosport Plus 4, but it doesn't have to be shipped to me.
Hope this helps.
Richard W. LSRM-A, G, PP, WS. IRMT
