For my Rotax 912S Mogas is the recommended fuel with not more than 1 in 3 fills of 100LL.
Using more 100LL fouls the plugs and valves.
There is a caveat with Mogas. The manual suggests mogas with low levels (or preferably no, ) ethelene based components, definitely never more than 10%. In fact in Canada gas companies are restricted to 10% but I think in the USA they go up to 13%.
Here Shell and Esso do not used ethelene based additives, the rest use between 7 and 10%.
These additives can degrade the performance of some of the seals in the Rotax. (You would think, would you not, that knowing they are recommending mogas and that mogas has additives, they would use seals that were resistant.)