Polycarb is very prone to stress cracking if exposed to certain solvents. Like acetone.
Spot on, make them nice and cloudy, you can polish them, automotive cutting and polishing paste like 3m or farclar ( however its spelled, yellow bottle) and a buffer with a sponge, i used to use white, slightly harder, keep wet its suprising what you can polish out.
Changing them is trick or if youve corded in a windscreen not so bad, plenty of silicone spray and warm the rubber in a bucket of hot soapy water first, its a 2 man job, one to hold it if you dont have suckers and one to pull the gasket in.
If you fit new ones fit proper polycarb as mentioned there are several manufacturers of it, i beleive theres a scratch resistant i was told about, similar to spectacles, some coating.
We had a fair number of cncs, im sure the fanuc robodrills had glass, laminated triplex.
Ive gotten scratches out of them with a glass polishing kit off an auto supplier, even came with the buffer for a couple of hundred, it worked on my house windows (argon filled tripple glazed units arent cheap.)
Mark
