Have 2 Manitou forklifts, M50 - 4, brakes suddenly fail completely. Not leaking oil, reservoir full, but air in system. Is there a way to find where the air is getting in or is it necessary to replace entire brake system? Since parts are a long way off and a long wait, it would be better to be able to find and repair problem quickly and without complete brake system replacement. These machines are down as they are obviously a safety hazard, have operators standing around with no machines, but don't have time to fool around checking the many possible places that air might be getting in. Has anyone had this same problem or experience with these machines? Any obvious places that are more prone to wear or failure? Thanks.