Yesturday i have clean my ZForce and i have seen oil the engine. The oil came from the vent tube from the rear diff that is attached over the engine head.

Anyone have ever seen this ?

[2015 Z Force 800 53/Trail EPS]

No but that means it either has water in it, it is getting very hot for some reason, it's very overfilled...or you have had it on it's side at some time.

No water and the Level is fine.
1000 km on that Motul oil .
I will change it tonight and check it on my next ride

I'm having the same issue with mine. Just curious if the diff oil change you did fixed the issue?

[2015 Z Force 800 53/Trail EPS]

I'm having the same issue with mine. Just curious if the diff oil change you did fixed the issue?

Change it...and don't over fill it.