Ian,

I may not be offering any new information here, but let me suggest the
following. Clean the sealing surfaces, then close and very lightly
seat the valves with your bolt-knob. Before putting in any water, take
a chap stick and apply fenerously around the edges of the seal. While
the wings are filling, work any excess into leak points along the seam
gently with your fingers, being careful not to unseat the valve. I've
had success with this... much more so than applying chap stick,
vaseline, and other sealants to the surfaces before closing. After a
few such applications, you shouldn't need to seat valve, assuming
there is ample tension in the closing mechanism.