I had a similar problem last year on my 2017 800.  The threads on the primary clutch shaft stripped when took the primary off to change the belt.  I had to replace the clutch shaft and housing. 

Those pics brought back memories.  Not a difficult job, but CFM definitely needs better metal.

...and how long to you have to hold the two buttons down?  I've held mine for 60 seconds and nothing happened.  No matter what combination of buttons and ignition I do...nothing happens.

I installed the fuel filter "catch can" this afternoon and am happy to report that I no longer have any gear oil leaking.  More testing is needed, but the initial results are very good.

Thank you both for the feedback.  I'm going to take the advice from both of you.

I'll change the fluid to Lucas Synthetic 75w90 and I'll install a "reusable" motorcycle fuel filter with the filter removed.  This should allow for about 2-3oz of fluid to be collected and returned to the diff before it starts puking out the other end of the vent tube.

https://www.amazon.com/gp/product/B0753F6PF4/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I just picked up a 2017 zForce 800 Trail and this is my first CFMoto.  Whenever I go for a ride I have gear oil leaking from the rear diff vent tube. 

I drained the rear diff and refilled with exactly 250ml of 80w90 gear oil (per the manual).  I put on a new vent tube, went for a ride and I am still getting fluid leaking.  I did a quick 6 mile loop with speeds constantly between 30 and 45mph.

I'm at a loss as to why this is happening.  I understand if the diff was overfilled or had water in it, but neither is the case.

What am I missing?  Do zForce just puke gear oil or what?  I something else wrong that I'm not thinking of? 

I'm starting to second guess my purchase.