I go with the 4000, it does not turn yellow. The silicon can hold, or it cannot hold--does vary. My own experience with the butyl tape is that unless you can keep the screws and bolts tight, eventually water and dirt will get under it. I know a lot of folks like it--and it is certainly easier, faster, and cheaper for the boat builders to use....but then again, most boat builders do not properly put in solid glass or epoxy potting when they put fasteners thru a hull, into a cored structure.