Another tip with Coin slots: An Aussie 10c coin is about spot on to a US 25c coin. So if you have a machine that is set for US 25c, try using Aussie 10c coins. All you probably would want to do is replace the tables with easy to get US 10c labels, and leave the coin mechs alone.
...now having been to the US many times, I only once tried this in a coke machine just to test it. All but one coin was a Aussie 10c coin. If all US coin mechs have that margin of error, then playing pinball in the US could be really cheap for unscrupulous Aussies!
Back to the thread. I have no idea how how to polish up plastic, but I would have thought that is what Novis was all originally about.