Oil leak

I had a similar problem on my pusher gyro 912.  Shiny liquid stains was on the prop. There is no cowling on my engine sitting behind me. 

One day when I  was carefully doing a preflight I discovered one of the small water hose clamp had somehow moved from its proper location. You might be having a small water/antifreeze leak. 

Buy some foot powder desenex brand and apply to area where you suspect oil is leaking from. You can buy one of those rubber plungers used to clean ears to help spray in the suspect area by first sucking some powder in plunger. Run engine, shut down and see if it's from the seal. You can do same to other possible suspect areas later by process of elimination. 

Don't use baby powder since it contains I thing petroleum based product that may damage rubber parts I heard especially on tire inner tubes where one should use tire tac only in tire before inserting inner tube. 

I have used this method not on rotax engine to find oil leaks which sometimes it's the last place you suspect. 

Hope this helps but if it not a good idea on a rotax engine,  I  am sure others with better experience and knowledge will advise.