Beneteau 321 Water Tank Sealant

[Plangstraat]

The water tank on my Beneteau 321 is leaking at the tank cover. I'm not sure what sealant to use to repair the leak around the cover. I want something that will form a water tight seal but also want to be able to remove the cover in the future if needed. Any thoughts?
The pics below show the cover and the current material that was used to seal the cover.

[SFS]

I used 4200, which will allow access again, though I don't expect it to be easy access. Be prepared to replace all the screws. Several of mine broke off due to corrosion and had to be drilled out. For those, I went to the next size up.