Lead deposits build up over time. 800 hrs. on this engine is nothing. Lead deposits will eventually build up on piston heads, in the crank case, on and in the piston rings, in the valve guides, under the valve seats. At some point usually during the life of the engine some parts may need dis-assembly and cleaning where someone using 91 oct. won't need it. The gearbox overload clutch is made up of 16 plates encased it their housing. The lead infiltrates this housing and fouls or clogs these plates. This prevents the clutch from working in a prop strike situation and transmits all the energy to the crank shaft which usually causes it to twist instead of the clutch doing its work. Time to replace the crank then. During the gearbox inspection (at 600 hrs regardless if you have a 1500 hr. or a 2000 hr. TBO) if you use 100LL the clutch gets torn down and all the lead deposits get cleaned out. You can't do this in the field and must go to a distributor.
All the guys I know toss the plugs at 75 hrs. We were taught that in Rotax school. Like you said at 100 hrs. they start to suffer.
You could run this engine on the original 3 liters of oil for many many years, but who wants to do this, eventually at some point something will happen. Same with lead eventually you will have some extra cleaning and there is no way around it.
Mlock,
Did you have the clutch torn down and cleaned or just the guy who opened the box up just look at the exterior of the clutch housing?