I don't have a Beneteau ST but can sympathize with your rudder leak problem. My issue with my Hatteras was that because of limited access, I couldn't get much torque on either the tightening or lock nuts, so the rudders would leak and I'd see it in the bilge. Out of frustration, I removed the flax gland assemblies and installed PSS dripless seals. This was five years ago and no problems.