This article is from the VW Technical FAQ, by with numerous contributions by Jan Vandenbrande others.
A: 3M manufactures a material called "Flexible Parts Repair Material".
It is a 2-part putty that is essentially a rubber Bondo. I [Craig] have
used it several times and am quite happy with it. I believe that
the kit costs about $15.00 at your local body shop supply store.
I [Jan] have used Shoe Goo at times to fix portion of my chin spoiler.
Works rather well.
 
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