Try removing a portion of the goo with a terry cloth dabbed in some olive oil, or vegitable oil, and see if you reach clean plastic surface. The oil will prevent loose goo from re-adhering to the plastic since the goo blobs become coated and "neutralized". I have used this method to remove very sticky labels from plastics before.

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'78 300D 310K Maple Yellow / Bamboo
'87 300D 81K Barolo Red / Safron (RIP @ 113K)
2003 E320 34K Pewter/Charcoal
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