WOW are you guys friggin cheapskates.
The OP is describing one of those weird, annoying, awkward situations that comes up from time to time.
The guy has no business asking for the game back after a decade but he'll be all butt hurt over it if he doesnt get it back.
The only thing to do is give the game back. The OP will have to see the guy from time to time, it's not worth the annoyance to keep the pin.
I think it would be acceptable to swap the old parts back in, there is no need to make a present of the new parts to the indian-giver guy.
The difference between being a cheap prick and being generous is maybe $10K spread over your entire lifetime.
I think the OP did right. And, irobot, I think you're being the "friggin cheapskate" here! "Swap the old parts back in"? Classic example of a cheapskate! The friend loaned him the pin, not asking for it to be repaired, just a FREE loaner for 10 years, with the only condition that it be eventually returned rather than sold by the OP. That's a free loaner that has VALUE, and no repairs were requested. It's pretty clear to me (and to the OP, who did the right thing) that the OP did the repairs voluntarily, and received the benefit of playing the machine for 10 years with no request for "rental" money.
I have a pin in a similar situation. Family moved from another city, and I had no room, so the EM I had at my parents' house was loaned to my local friend. If I move and have more room someday, I may ask for the pin back. He knows this. But he gets to play it in the meantime. And I may let him keep it as well. Dunno. But I would be pretty pissed if he sold it, and he wouldn't sell it because he would either hold onto it or return it.
It's not a totally uncommon situation with pins and arcade games. They take up a lot of room, and I know many people who "lend" them to friends for an extended period of time. The person doing any repairs does so for their own benefit as they can play the repaired game. In the OP's case, the game worked sometimes, a little rough, but wasn't a busted-up project that needed major repairs to be used at all.
Kudos to the OP for returning it. I'm sure he was happy to be able to play it for 10 years. And I'm glad I don't have friends like the cheapskate commenters here who suggested demanding money for the repairs! (At least no friends that I would lend anything to!) Heck, the family friend could've demanded rental fees for use of the pin all those years! The benefits pretty clearly balance out here.