If alchohol wont clean them,Time to get new windows. Mori has specs on window life, think after 5 years the windows degrade to 50 percent of impact resistance. They have put a lot of time and money in to studying guarding and windows. The new machines even have timers to alert you. Mori probably has the best safety windows on the market btw, it started with a guy getting hurt real bad, he's in a comma still after 15 years. Owner of the shop had lexan cut and made his own window on a old sl. It was a huge mess for everyone.