ive got a 1996 201 pro xl ball is going flat changed ball still the same .boat has two tanks with lever on wall beside drivers seat. someone mentioned to me it could be these valves or valve.im trying to figure out how to get at them and where they are located.iknow the gas tank is under the seats and up the back.there seems to a be a piece of decking that might come up right behind the seats if thats where these valves are but i cant find the screws any help would be appreciated.thanks pat