Run continuity to the boards. If continuity is ok, you probably just need to replace the buttons. It's not rare to have to replace buttons this old even if the game isn't a rust bucket.

Do not hose them down with wd-40.

Sounds like this Hook you picked up spent some time at the bottom of a lake. You are gonna have to replace a lot of stuff.

Also...rattling around my brain...there's a coin door interlock switch on these games, if that isn't working correctly it could cause the buttons to not work I believe.