eraser---I have a 3w with a similar, but not to your extent, problem. I did the line from the diaphragm thin with no success, in fact made it worse. I could not find an area in my plane that was not pressurized.
What I ended up doing was making a box about 1"x1" out of balsa. Then you put the the diaphragm vent line into it. I made sure mine was pretty air tight. Problem solved.
It is worth a try and costs next to nothing