Not one 80's SS Pinball was painted in a Gloss finish. Back in those days, manufacturers used lead based paints. The stencils were brass and held against the machine and a THIN coat of paint was applied against the base. One key aspect to remember was that pinball machines were a commercial product, designed to make money. The finish would have been whatever was in the paint shop at that time. But is was never Gloss. When I match cabinets, I take the cabinet to a professional paint supplier with 30 years of experience. There is no uniform color or finish that is 100% consistent. But one fact remains - the finish is either a satin, or semi gloss (reds on Gottleib EMs as an example). Never a full Gloss.
On occasion I do see SS cabinets repainted with a Clearcoat applied. Not one single SS cabinet was ever clear coated. Not one cabinet was ever made of plastic, which is what a clearcoat on a cabinet looks and FEELS like.