Anyone know a good plastic cleaner? my friend has a porsche boxster and needs to clean the rear window on the convertible top.

any good cleaners?

I have used Plexus cleaner with good results.

Plexus Cleaner Link

I've used two excellent products,both made by 3M,on my 1999 SL500.
3M-part no.39017. Plastic cleaner. Removes fine scratches.
3M-part no.39010. Plastic polish. Cleans and protects. Restores optical clarity.

Easy to apply.

Meguiars PlastX, will sort your problem.

PlasticX works for me too.

is it fine scratches? or is it like mold on there, or what?

I use Meguiars PlastX if there are scratches, then plexus to clean or polish very vry mild scratches.
How to clean and polish plastic windows