5200 is a polyurethane based "permanent" sealant; (like the Sika Tim mentioned, I think. We don't get a lot of Sikaflex products here in the US except for construction adhesives.)
4200 is 3M's "removable" stuff. Also polyurethane based, fast cure (24 hrs.)
3M 4000 is a polyether sealant/adhesive (their term; it sounds like what a lot of companies call "caulk"); white only, 24 hr cure.
Just noticed that West Marine does carry Sika 291 and some other flavor. Didn't see that before.