Hi Phil,
A mold of a cast from a mold just compounds any imperfections.
The exhaust diaphragm does rest with some slight pressure against the rim of the exhaust horn. When you exhale, the diaphragm lifts just enough to allow air to flow over the lip of the horn and escape. My silicone casts seem to seal a whole lot better than the original diaphragm. It appears the silicone has greater elasticity memory than the original diaphragm, seats better, and pops back into place more readily after the air is exhausted. You may be correct that I have nothing to worry about but the slickness of the silicone (at least the batch I currently made up) just concerns me that one good hard exhalation might pop the flange on the diaphragm out from under whatever is used as a retainer. A good glue might prevent that but i would like to have some redundancy in holding power. I think I'm on to a good thing here but I got a bunch more 'spiramentin to do.
All suggestions welcomed.
Mark.