I fix these things as an avocation. Aquastop valves seldom fail by themselves. There are two very thin o-rings at the base of each valve stem.If they dry out, the valve can be hard to seat into the receiver. And too much pressure on that red lever will snap it off, sooner or later, and could distort those seals enough so that leaking may occur. A small amount of silicone gel will soften them up and will enable the valve to seat with"as new" ease. I have also found that continuous and over-use of the primer assembly can cause a very small o-ring situated within the primer assembly under the cover can get distorted or broken and allow air into the canister which will expel thru the outlet nozzle...constantly. After checking the motorhead seal and the rubber adapter connector to the intake tube with no improvement, I am pretty sure that a change in that little o-ring will solve the problem.