Anyone had bad experience with Zpeed heavy duty slave cylinder?

gsg740

I heard lots of good reviews about Zspeed heavy duty slave cylinder.
Last week, we tried to install a clutch kit with the Zspeed HDCSC. Everything worked out smoothly. However, after we finished up everything and were trying to bleed the clutch. We found the bleeding screw on the slave cylinder won’t be able to seal the system. We tightened the screw as much as we could, but it leaked when we pumped the clutch pedal. No pressure could be build.

We took a look at the bleeding screw. It seems the system supposed to be sealed by two pieces angled metal surface, much like tightening tapered lug nuts into the wheels.
It’s hard for me to believe the system will be sealed without any rubber ring. Is there anyone else had same issue as I had or did I miss something during the installation?

Thanks a lot!