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Be sure to gently wash the outside of the top before doing anything else, flooding with lots of water. You don't want to be grinding grit into the plastic.
GM sells a glass cleaner that is approved for the lexan top and also works well on other clear plastic, like the gauge faces.
The cleaner comes out of the spray can as a kinda white foamy stuff, doesn't look or smell lke it would be very effective. But I've stopped using Stoners on my real glass, the GM cleaner seems to work just as well and won't attack plastic.