I clean my isinglass before every season and it seems to help a lot. I usually wash with mild detergent and then use a commercial product made for this. There are cleaners and polishes and combinations of each All work well and there is a Mil Spec. that some comply with. After I polish with a soft cloth I buff the panel using a oscillating automotive buffer. Sounds like a lot of work but they stay cleaner longer. Since I shrink wrap the boat the panels are taken down each year. I made up a removable table that I assemble in the salon to get this job done, It is just strapping and (3) pieces of 2'.4' pegboard available at Home Depot. Just cover the top with a drop cloth or soft towels. Like someone else suggested it is easier to get them replaced, then stay ahead of it. I usually rinse the boat after each use but have found that the new diesel causes real problems to this type of plastic. I have the two back panels in the shop for new glass due to this, and they are only five years old. My canvas gal says wash any isinglass with soap to get the effects of diesel fumes off. My engines hardly smoke at all so I was unaware of this problem. Tom Egan