Mr. Clean
I recently did an office that had two 4x8 sheets of plexiglass seperating two interior offices. It had already been scratched and I wasn't sure what to use on it. When I got to them I had forgotten that they were plexiglass because I had been cleaning windows and thought they were glass also until I started scrubbing them and remembered they were pleiglass. I stopped immediately but the owner told me not to worry because they were already scratched. I continued cleaning them the same as glass, using gg4 and a washer and squeegee. They seemed to come out fine with no damage. Don't know if that is how you should clean plexiglass, but it worked for me that time. I would think that you just want to be sure that your washer, scrubber, whatever, does not have any debris in it that could scratch the plexiglass. I know you cannot use solvents like oil flo because it will cause damage to the plexiglass.