The 3m 4000 will not yellow as the 5200 and 4200 do. Loctite has a product very similar to 3M 4000, but much cheaper ( Loctite PL Marine is $13 for 10 oz at Home Depot) Neither of these are polyurethanes, but polyether compounds. They are fast cure, remain flexible, do not shrink and have very good adherent properties. A bonus is that they do not attack plastics, so can be used for bedding of a number of plastic hatches, port holes etc.