Is there a reason none of the appearing post mechs (2x Stern, 1x Williams) that Pinball Life sells would have worked?

Another possibility for clear coat that I've had success with is the Parks Pro water based polyurethane that is used for floor finishing. No odor, doesn't go bad, and so far it's held up to well over a thousand games on Polynesia, my tiki retheme EM. $43 for a gallon at Home Depot.