you have to remove all the fluid film or else the paint wont last. it may appear to stick but it will fall off eventualy. this is what i would do with your tow eye...
if you have access to air tools all the better if not the old fashioned way will work...
either by air sanding with a 24 or 36 grit disc, hand sanding, wire wheel in a drill, remove as much of the paint/rust as possible. get the hook as close to bare metal as possible. grab a can of rustoleum professional grey primer in the spray can, give the hook 3 very light coats of primer letting it dry in between each coat. let it cure for a day then paint it with whatever metal paint you want then once the paint has cured coat it with fluid film
i go threw that rustoleum primer by the cases come nice weather. the stuff is amazing. 99.9999999999999+% of the time when the surface you use it on gets the paint chipped only the paint gets destroyed. the primer stays unharmed