I hate to say this but sometimes an old pinball machine is simply too far gone to salvage and restore – at least not with significant investment.
Probably any machine in any condition could be brought back to life, but at some point, you’d have to replace every single piece of the machine.
Much better to find a game in “decent” condition and then take it to exceptional condition than to find some game that held together with rust.
Take this game, a 1968 Gottlieb “Royal Guard” for example posted on Facebook Marketplace for a laughable $300. Only 2,900 of these were made, yet I seem to see this title come up for sale often. One wonders how many survived especially if they were stored like this one, in a leaky shed.
Right off the bat one can see the broken playfield glass. Replacement cost: $50. Then there is the rusty coin door – sometimes surface rust can be sanded off and maybe plated. Or a new or used coindoor could be found – $50. But surely this rust must be a sign of more rust to be found inside.
Then there is wear on the playfield which would require touch up with a delicate hand. New rubbers $30. Flipper rebuild $40. New pop bumper parts $40.
Then you have the cabinet condition. One would have to determine if the cabinet is ok or would need a repaint. The backglass is shot so a reproduction would have to be secured at $300 plus shipping.
This shot is very revealing because you can see the rust extends to the inside. The legs are rusty so they’d need to be sanded down and repainted or replaced with new ones at $60.
Even worse is the mouse chewed paperwork and schematics indicating mice probably live in this machine over the years. Mice can chew up wires making the overall restoration possibility that much harder.
Can this machine be restored? Probably but at what cost? Certainly, the restoration would cost more than its value.