Ive been reading about looking after fins over on mypaipoboards.org . Ive left my summer fins out in the sun for days on end, letting them sun bathe for hours until there scorching. Their into their? fifth year and showing signs of fading and a few little stress marks on the straps, I really don't want them to snap as I hate throwing stuff away. The 303 aerospace protectant promises to be water based and has good reviews so I'm going to give it a go. You can find it on ebay..
Definite improvement...straps seem more flexy and the rubbers nourished!