Plexus is what you need. This stuff was originaly developed for aviation winsheilds and has now made its way into the marine and motorcycle industries. The last several helmets I purchased had stickers saying to only clean the visors with it. I have used it on convertible windows since I first found it about 10 years ago. Any good bike shop should have it or on line at www.plexus.com
Brian 67 Bird Convrt. under construction, 67 Tempest 428 Covrt. finished(?)-owned 35 yrs.