flushmate run-on followup
and the winning advice goes to e-plumber. This, of course, made Mrs. Notaplumber jab me in the ribs and say "I told you so" as she had told me that already.
Flushmate did not send a replacement pressure vessel, but a "duckbill". This is probably a 10 cent rubber part that regulates the amount of air induced into the system. 30 seconds to replace it and it works like new. The old one looked like it had been dropped in a vat of battery acid. A note with the new part said the original parts were found to be unfriendly with chemicals found in the water supply and that the newer parts were less prone to wear.
Thanks for the replies.