@Grover70 - My main reason for sealing the gap in the anchor locker is to protect the exposed fiberglass. In the original boats there was a huge gap between the hull and the actual anchor locker insert. This allowed a ton of water to pour in directly into the changing area. On my boat it looks like they finally fixed this by installing the anchor locker directly against the hull (no visible gap). I still, for the life of me, don't understand why they just didn't run a drain all the way through with a sealed flange in the anchor locker (that part might cost all of $5). I agree, most of the water coming into the changing area now is either coming from the bilges, the fish locker fitting, or from too much water on deck (washdown or rain).
However, if this gap is left untreated, water can wick in between the fibers and can cause some serious damage in the long run (usually the gel coat will start blistering). Capillary action can pull water into the surrounding area way farther than one might think and it is impossible to dry out. Again, not sure why Yamaha's design leaves any untreated fiberglass directly exposed to water.
With that said, this fix turned out really well. It was super easy and I was able to retain the original fitting. My only suggestion is to make sure you do this while you have another 4200 project ready to go. That is the most expensive part as it is not a big enough job to waste $15 on a single tube (4200 does not store well). I really wished they made a small tube of 4200 (like they do with 5200).
Hope this helps other FSH owners. Happy boating!