Really open the crankcase for this?

Sorry, the bulletin is an SB, not an SI, it was released in 2004.  The issue over time was the main motivation for the new ignition timing and soft start system Rotax introduced in 2010.  For the most part this has solved premature failure of the sprag clutch.  Use of leaded fuel and running rich mixtures can still create problems however.  Engines now are fitted with the housing for the sprag having 2 holes to clear most lead buildup and keep it from binding up the spring and cams inteerally. 

sorry for the spelling errors, spell check apparently does not like "sprag"and wants to spell it with an added ue on the end.  Odd that. 

Cheers