rear window funk

[robert williford <RDWILLI@VM.SC.EDU>]

the convertible top on my 73 b sat rolled up in storage in a barn for
quite a few years (along with the car).  the plastic rear window has
some really strange brown stains that don't want to come off.  i've
tried glass cleaner--it did a great job on the rest of the window
but didn't touch the stains.  any recommendations on the best
thing to use to clean this crap?  i'm wary of using anything
terribly caustic or abrasive as i'm not sure of the effect it will
have on the plastic.

thanks,
-robert