Have done mine twice in past 3 years. Total PIA job to do. I suspect that the seal has failed because I didn't remove the acrylic lens completely and rebedding. If you break the lens attempting to remove it, you are facing $$$$ to replace it. However, I was meticulous in moving all the adhesive and sealer from around the lens perimeter, sanding, and cleaning. On the first repair, I used the same stuff that Beneteau used. On the second attempt, I used Sika primers & sealant. ( fairly expensive stuff because the primers are costly) Sika started deteriorating in months. I am due to reseal it again; plan to use Dow 795UV this time. Estimate approximately 10 hours to completion by the time you remove the old sealant and adhesive, sand, clean, mask, apply primer, and reseal, then cleanup.
Not a fun job.