I can shed a little light on that system. Instead of a master cylinder and brake fluid it uses a valve and hydraulic oil. The valve has a hose supplying it with low pressure oil (500psi ?). There is a bypass return line from the valve and the steel brake line going to the wheel cylinders. When you push the petal it should be closing down the bypass return and building pressure to the brakes. The problem I had with one of those was that in cold temperatures and thicker oil the by pass could not keep the pressure way down so there was slight pressure in the brake lines even with your foot off the brake. That would cause the brake shoes to drag. The only cure was to install stronger brake shoe return springs. Maybe changing to a lighter oil would have helped.