Nature of the failure is the flap falls out of the transducer tube and disappears. Hence we get a massive gush of water each time we change over the transducer for the blanking plug which is generally weekly in summer.
The water is easy enough to clean up however we would prefer to keep as much water out of the boat as possible for obvious reasons, hence wanting a flap that works more than once or twice
The company that has done the installation for us is one of the largest Raymarine installers in the area, and we have used them for fitting out of our past 3 yachts we have owned over the years. So I don't think they are installing it incorrectly.
Furthermore they are aware of all the tricks to look for during the installation from the following information from Airmar;
"The risk of the original valve becoming dislodged requires the ring to be positioned with the gap positioned directly over the valve hinge. Assembly instructions include the orientation of the snap ring with ring gap 180 deg from the valve hinge. An incorrectly positioned ring could occur during assembly, or during post-delivery handling. The ring can be rotated by hand from the "as assembled" orientation (180 deg from the valve hinge) during installation or subsequent handling. Please note, that with the snap ring gap located over the valve hinge (incorrect placement or subsequent manual rotation), the valve body remains securely retained within the housing, but includes a higher risk of failure due to the size of the snap ring gap and valve hinge. "
As indicated in my original post I'm curious to see if others have had similar issues with this transducer.