Yes, it's not leaking there. I just swapped a bunch of parts from the 400 to the 440 and it got somewhat better but still leaks. It has a small leak letting air into the fluid nozzle (2-1), a small leak around the packing nut (3), and a small leak around the air valve shaft (12). If I lightly press back on the air valve shaft (12) then the packing nut leak and fluid nozzle leak stop. If I press forward on the air valve shaft (12) until it's against the trigger, then it's own leak stops. Seems to me like the air valve seat (7) isn't sealing allowing air to get around it and leak through to the nozzle/tip area. I don't think the packing nut is leaking once it gets moved the slightest amount, possible a worn needle in that area?
Is the air valve shaft (12) supposed to be constantly pressed against the trigger?