For Koji, location and driving the splitter down. He isn't able to do that at this point. he has a dead arm. I'd still bring him back for next year, though we need a different closer.
When the Sox signed Koji in 2013, he never was expected to pitch so many games, much less closing. A year+ later, him and Tazawa are tied for most games pitched since 2013. I think Koji is still a good reliever, but can't be trusted anymore. It's age catching up with him.
Victorino is a piece of broken glass, and with 1 year left, they should bite the bullet and deal him. I don't think Victorino has anything left. He has a lot of different chronic injuries, hamstrings, back, and who knows what else is awaiting.