Rotax Service say:
“It is possible but not recommended to use 100LL AVGAS, since the the lead content is like cholesterol to your engine: it will accelerate wear on the valve seats, create deposits in the combustion chamber and sediments in the lubrication system and gearbox. Increased maintenance is necessary to compensate. Unlike “conventional” aircraft engines, lead is absolutely not essential to the proper lubrication and operation of a Rotax 4-stroke aircraft engine. The increased octane rating also has no marked advantage for the operation of your engine.”
When using AVGAS 100LL for more than 30% of the time then Rotax suggest that the oil, oil filter, spark plugs & gearbox will need more maintenance than if using MOGAS or AVGAS UL91.
Monitor consumption of differing fuels. Rotax reduce the oil change intervals to 25-50 hrs, replacing the spark plugs every 100hrs. See picture below; the lead covered slipper clutch. The slipper clutch ought be inspected every 600hrs.
AVGAS 100LL use = more maintenance
