Best Sealant to Use for this Application?

[Belle]

We have a 1978 Argosy MH that developed a rainwater leak. We have narrowed the main problem to the top of the door frame where there is a gap of about 1/16 inch between the door frame and aluminum skin. When pushing fairly firmly on the skin, the gap will open up to about 1/8" then close when pressure is removed. It appears that original sealant may have been 'Alcoa' sealant although we may have re-sealed this ourselves 20+ years go.

We have a fresh tube of aluminum pigmented gutter seal (Ply-Gem formerly "Alcoa") . Would this be an appropriate sealant for this area or is there better choice considering the size of the gap and the inherent movement from the door opening / closing? We appear to need a good sealant and adhesive with elongation properties for this application. There is a thread regarding sealant for various exterior areas to be sealed but not sure if these would apply to a door frame. Par Bond is an option but that is out of stock at most locations (Vintage Trailer Outdoors mart, etc.) I am a little leery of Sikaflex 221 due to the permanence of the product although the area to be sealed is maybe 12" long on the side of the step light hood.

Suggestions?