I throw myself in your mercy again as I can't find a link.
It's a fic where the Winter Soldier gets in the way of magic aimed at Steve and ends up splitting into Winter Soldier and pre-Azzano Bucky. Bucky ends up helping WS get sorted and they turn themselves in to get back to Steve, who helps them escape from SHIELD. I can't remember the title and it's driving me nuts!
(I originally came across it via a shorter pornier fic that used the idea of James/Steve/Bucky from the original one. I think it was part of a series of prompt fills, maybe? I can't remember the title of this one, either.)