M&R 1996 Gauntlet ?

I own a 1996 8s 6c gauntlet "s" which I need a little tech support with. My problem is head #4 will flood the screen with no problem but when it goes to clear the screen it clears it incredibly slow. The valve that controls it is open all the way yet it doesn't help. Another symptom is when the head sits in the back position it sound like air is leaking from the valve block assembly but when I select the head and as a flash station and it moves to the front position the air leak sound goes away. Does anyone know what I should be looking for and how to fix this ? Thank you in advance