I've read a lot of posts about top coats and much of Vids guide. I'm wondering if people can help guide me with some basic identification. Attached is a close up of the playfield. I'm trying to determine what the top coat is on this. Looks pretty original to me, and top coat looks like it was brushed on. Anyone know what I'm looking at here? Would the original to pcoat from Gottlieb have brush strokes?

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I should add that I took some 90% ISO and ME and scrubbed hard on some lower pristine finish. Didn't seem to remove the top coat as I thought it would.

Great help guys. I'll do some test swabs with different solvents to see what it is. All the dirt is in that top coat, so I'd like to remove it and maybe I'll be able to just wax it or top coat it again.

Thank you. I'm hoping it's water based poly, but we'll see. I'm using a lot of caution.

A little update for anyone who is curious. I tried a few test areas under the metal apron at the bottom. That top coat didn't budge with xylene, which tells me it was not water based. Lacquer thinner cut through it, so likely a non-water based polyurethane. With some careful application, that coating can be cut through without getting into paint. I'm sure at times I got into the original top coat a little, but I'm just trying to get at the suspended dirt in the poly. Results are pretty good so far and I plan to stop at "pretty good" and not push my luck. Then some Novus II, then a good coat of wax.

New question though: There are finishing nails behind some of the slingshots. Did gottlieb do this or another "clever" owner?
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That's good to know...thank you