Topping off with XPS in 912iS

For what it's worth:

XPS is a full synthetic oil

Aeroshell Sport Plus 4 is a semi synthetic oil.

Personally I would not combine them.

As for changing from Plus 4 to XPS -Cant see the point in a "flush" - I would do a usual oil/filter change, just use XPS in place of Plus 4 and then a second oil change, say 5-10 hrs later, again with XPS.

Rational -

Do not mix oils of diffrent chemical makeup.

Flush may remove most of the old Plus 4 oil however some flush will remain to contaminate new XPS

By doing an oi/filter change you will be removing almost all the Plus 4. The small amount that remains, will be highly diluted by the replacement XPS.

Interim oil/filter change at 5-10 hrs, using XPS, will further dilute the already small amount of Plus 4

Alternative: Drain all Plus 4 oil from system. Replace with XPS & do a full oil system purge. Future service intervals as per Rotax recommended.

Sean is correct. 

There is a procedure in the MML that works.  I would follow up with an additional oil change at 25 hours after to be sure all traces of the offending oil are gone.  

The XPS must be used for the type 916.  We have already heard about some engines with the Shell sliping the overload clutch on takeoff.  While it cant be sure that is the issue Rotax has advised any engines with slipping and the Sport Plus 4 in a 916 will not be covered.  

Cheers