Thank you so much for any help you may give, but I know what I remember from this quite old fic is really vague:
1. Tony liked Clint's "crinkly smile". He thought that Clint should smile more, and there should be "more crinkly". Tony definitely tries to 'fix' Clint like he 'fixes' his bots. He wanted to help, to fix them, even tough I have the vague memory that Tony either rambled a lot or did not fully understood humanity.
2. It was slash. I don't think Clint and Tony were together, suspect actually that Clint/Tony was more bro-ship than relationship in this fic. But there was slash (99% of what I read is slash).
More than probably it was in AO3.
I'm sorry? There is literally practically nothing to go on.
Edit! Found: It's the first story in Dodgy Chinese