Cleaning gunk off the inside rear window

My rear window has a layer of gunk on it that windex couldn't clean.
I was thinking of using 409, now, but I'm worried about hurting the plastic
defrost decal.
Are there any precautions I should know?
Thanks in advance.
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Can you more adequately describe this gunk on your rear window? Can you scrape it off with your fingernail?
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On Fri, 22 Apr 2016 19:34:09 -0700 (PDT), snipped-for-privacy@gmail.com wrote as underneath :

Probably that film of hot plastic interiors leaching nasty stuff over time! Sprayway foam glass cleaner (USA) is pretty good for that but expensive at least in UK. C+
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"Charlie+" wrote in message wrote as underneath :

http://www.invisibleglass.com/
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