1976 Dodge Chinook - Exterior Question

[RinaBea]

Hi Everyone,
My husband and I just bought a 1976 Dodge Sportsman Chinook. It needs a lot of work! We are in the process of gutting the interior and removing broken hatches, windows ect… from the outside.

After we removed the windows and were scraping off the excess silicon/butyl tape, whatever was used to seal them, my husband noticed that whatever substance was in the upper channel (roof line) was hard as rock and cracked through out. This is our first Chinook and we aren't sure what the channels purpose is.

So the main question is does the channel need to be cleaned out and new 'compound' put in? If so what is the compound supposed to be?

Does this channel act as a rain gutter? Is it like a roof cap? Do we need to be worried about water leakage to the inside from this channel, ect…

Any help would be gratefully appreciated!
Thanks so much in advance.

Here are some pictures of the channel and what the compound inside looks like right now.