did you check the brake pressure at the brake line on the motor?
I would put a pressure guage inline on the brake circuit and see if the pressure is dropping when it gets hot.
check the fitting on the hose connection.
diagram shows brake line to RH motor and then to LH motor.
If LH motor is releasing then something is either wrong with the brake unit on the RH motor or its not pressurizing the brake servo.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.