The forward hatch leading to the crew cabin on my Sun Odyssey 51 has through hull handles. After a few years they started to leak ruining the interior ceiling etc.
I emailed Goiot to ask for replacement seals and possibly instructions on how to replace them. They never answered and I have to say that Lewmar does a much better after sales support than Goiot or Jeanneau for that matter.
Anyway steps are:
Remove inner handles, needed a puller to separate the aluminum handle from the stainless steel shaft. Removing the locking screws that was severely oxidized was done with an impact screw driver and a sensitive index finger.
The inner ceiling had to be redone due to water damage and rotting. Another project by itself.
The hatch frame had to be unbolted. It was seated with aluminum screws so take care. The frame was sealed against the deck with an adhesive tape that was cut with a thin sharp blade. With the frame off, unscrew the gasket box that is bolted from the underside. This design creates a lot of work for anyone that has to re-seal the handles since the whole hatch and inner ceiling has to come off, see fig 1.
The actual seals have to be hand made since Goiot was unresponsive. I used a 2mm think rubber sheet and hole pipe cutters to punch out a rubber washer that sealed tightly against the shaft, see Fig. 2
Also the seal between the steel gasket housing and the frame was redone in 2mm thick rubber using hole pipe cutter and scissors. See fig 3
I filled the housing up with marine grease to keep operation of handle smooth, minimize wear and overall water repellant.
Re-attaching everything is just done by reversing the order of dismantling it all.
Make sure to get good quality UV resistant rubber or silicone. I also tried O-rings but did not find any suitable size that would seal up and also fit underneath the locking pin on the shaft seen in fig 2.