Given the sheer age of the thing it is probably pretty straightforward inside. If it manually spins the wheels then it probably wouldn't be too hard to repair. But if it uses motors, then forget it, as it may have one or more of them burnt out, and do you REALLY want to spend money trying to replace motors when you can simply buy a late model jap skill slot for $100 at any auction?
My personal suggestion? List it on ebay with a start bid of $100. If it sells then good, you can use that money to replace it with a late model, reliable, japanese model.
If it doesn't sell, then crack it open and try the basic stuff, look for burnt up stuff, replace capacitors and such. if that doesn't work, then pull the parts you want, and then part the rest of it on ebay.
Spinning slot reels on a Mame cabinet marquee might be pretty cool!