Hey guys I was one of the first ones to buy a ZForce at my dealership when they started selling cfmotos. (Big mistake I guess)
So at 700km the whole engine oil came out they the cases. Lucky I was putting it on my trailer after a few hours riding. Wasn't impressed but hey shit happens right. Took to my dealer everything got fixed under warranty (expensive job so I was ok with it) mechanic said they had an upgraded gasket. Was ok for a year (I don't ride that much) then at 1400km again the same problem.... Another month without my machine. This time they said they were gonna try to make a gasket with special silicone or etc or whatever. Now at 2000km same shit again. Took the machine in to the mechanic but this time I'm not happy at all and ask them isn't it time for a new engine? Every year the same problem? Anyone else complaining about the same? Iv been defending cfmoto since I bought it and "selling" it to everyone but now I'm starting to think it was a big mistake...

Sorry for the long text.

[2015 Z Force 800 53/Trail EPS]

Sorry to hear that is happening to you. Sense the creation of the ZForce 800 is 2014 there has been relatively few case halves seal problems including the 800s in the CForces but there has been a few and all I know of were corrected by either a new gasket or case itself. Now that problem jumped dramatically with the new cases on the 1000s in 2018 where at first it was almost 10% has some kind of leak either to the outside or between the transmission and engine sections (The 800s were a shared sump where the 1000s got divided). Those have returned to near nonexistent levels now though. As for the ZF 800s, I haven't heard of any with case problems sense 2018 however in 2019 on the first CForce 800s Xcs with the new non-wet clutch 800s there were a few case leak issues.

I'd say it's time for a new complete engine or...a different machine for you. Have them check the engine mounts...they are rubber mounted not only to help vibration but if the flex wasn't there the stresses on an engine case would be horrible. Something might be assembled incorrectly. 

Same thing happened to my fathers 800 ex.  He noticed a leak which was supposed to be fixed with an updated gasket.  Then almost a year to date it started leaking again. Worst part is he had hardly put any miles on it.  Cf moto would only pay for parts he was stuck with the labor ($1200).  The day he got it back he traded it for an Rmax 1000. 

I would push them for a new case.