Columbia - rub rail/hull deck joint??
I have a ''74 /columbia 23 that has an overlapping deck hull joint that seems to be "glued together (albeit not very well) and then Pop-Riveted. None of the joint is actually inside the boat so I don''t know about the aluminum channel.
I sail on inland lakes so haven''t worried about it much, but it ain''t much of a joint. It does work some in bad conditions and I have gotten some water thru the joint a couple of times; i.e. 20 gusting to 30 mph with 2''+ chop.