I think you need to give yourself a break and have a sigh of relief.. Junpei is well and alive. And I'm so glad to hear the good news! I guess the stories other people tell are true.. cats don't go far when they get lost!
IF you leave him there, he will probably be ok. IF you don't, who knows, it could be for better or for worse. Don't bathe him though, if his smell goes away, he will have to do catfights all over again to protect his territory as the other cats will think he is someone new. The limping is most likely the result of a catfight.
I'm so happy for you, at least you know Junpei is still alive and kicking! Don't go away to buy food next time you see him, just sit there and wait for him to come to you. If you have food, that will lure him in but don't hate yourself for not having food 365 days after the day he got lost!
I know you wanted to bring him home, but I see this as a happy ending. I hope you will too :)