Cleaning a Hales woofer

I sublet my apartment for a while and something seems to have spilled on a woofer in on my Hales Transcendence 5s. It's just a little bit, and may even be limited to the surround.

The woofer is polypropylene. Any advice?

First thing I would try and identify stain.Almost impossible I know....Try Q-tips with a little soapy water,maybe those handwipes...something unabrasive/aggressive.....not sure...if their poly,thats petro-chemical[oil]....maybe leave if no corrosion yet....sorry,no GOOD idea's here....HELP,good luck,Bob