Steve briefly looked at Bucky when he made that offer, but he wasn't too surprised by it. They were both desperate to get that arm fixed; he just didn't want to volunteer Bucky for this without his approval. But it seemed like he was willing to do it and he didn't think Tony would take advantage of him either.

And if he did, Steve would make sure to stop him.

He already knew he owed Tony a whole lot, which wasn't why he didn't bother to say something similar. But he was truly grateful for what he had done so far, he just hoped that Tony would keep going.