OK. I very carefully cleaned the seal and inspected it, and the seat and could see no reason that properly seated it would leak. Put the blank in and very carefully sealed it up and took it to 3M. Leaked like a sieve from the end of the housing with the seal. Inspected seal and seat post immersion and no obvious issues. Will have to contact divevolk when I get home. Just to clarify, I have been diving DSLR’s for 15 years or so. Don’t think this is user error - something is wrong with the housing.