Newer Tost hydraulic brake issue

The Tost hydraulic brake cylinder mounted to my stick failed on my last flight. I've emailed Tost, but so far no response, which certainly might be virus related and therefore understandable.

The brake worked fine before takeoff but before landing there was zero resistance when squeezing the lever. I'm 99.9% sure its NOT an issue with air in the system and just to check I flushed from bottom to top and no change and no bubbles exposed.

I suspect that if there is a check valve inside the piston of the cylinder that it has failed open. There is a swishing sound when the lever is squeezed as if fluid is being pushed through an orifice (no external leaks found) so this matches my hypothesis.

If you have actual knowledge of the internal design of this hydraulic cylinder, particularly if you've taken one apart, please message me directly.

Thanks,

Mark