Top Rear Window

["Edwin McCarroll" <emccarroll@mco.edu>]

My MGA top is in fine shape except for the rear plastic window which has 
started to brown.   I suspect that direct sunshine u.v. is making some kind of 
chemical change in the window material.   Any suggestions for cleaning the 
brown stuff off the window?    It can be removed by scratching hard with a 
finger nail.