I knew Steph would get involved here at some point, just thought she'd have a wrench in her hand /forums/images/graemlins/grin.gif..
Eddie, maybe you can sell your design for a couple hundred bucks...Its amazing what one can do if he really thinks about it..
Curly, I'm in a similar boat as far as actually doing one of these.. But, to my knowledge, its just a metal to metal connection(seal).. The minute size change of metal under different temps is plenty to create this seal. This is also part of the reason you need to add an anti cavitation additive to your coolant on a regular basis.. It reduces the scale, electrolisys and metal transfer that would cause a leak.. Like I said, I've never actually done one, but thats my understanding of it..