I rebuilt mine using a piece of truck mud flap.  I drilled out the
rivets, un-sandwiched the broken flap, inserted a new piece of good flap
material, then re-sandwiched it back together and bolted it where the
rivets were.  Has been working for a few years now.

I have it posted
http://kokopellisgarden.com/vw/
click on other modifications, then on mud flaps
Let me know if you need more info.
Ken