Check the velocity. Is he not-perfect-but-getting-better? Or is he not-perfect-and-getting-bored?

You want the former, you don't want the latter. Someone who's not perfect but listens well, is interested in improving, and is passionate about the company will likely soon be perfect, or as close to it as you're realistically going to get.

If he's not really into it to begin with, then it doesn't matter if he's perfect, you still don't want to partner with him.