Francois:

     We have had similar problems with those valves on our Optima over the years.  The leaks generally occur when
we switch from continuous flow to dual inlet system mode and we usually get rid of the leaks by repeatedly opening
and closing the valves and maybe hitting the leaking valve a little (this was actually recommended by a Fisons person
years ago).  I actually talked to a man named Phil Dodge at Precision Dynamics (the maker of the valves) about a year
ago about this problem.  The phone number was 860 229 3753 if you want to try to talk to the company directly and
maybe get a cheaper price or buy only part of a valve.

Roger Burke