I had the same issue back in 2018 and have a solution.

The head of the stud is actually a wingnut.

What I did was to heat the remaining stud with a micro-torch or a big soldering iron. When the stud conducts enough heat, the plastic will get soft, grab the stud with pliers and pull straight out.

I bought replacement stainless steel metric wing bolts, washers, and nuts from McMaster-Carr. Dremeled out the pocket to fit the wing bolt head, placed the bolt in and topped off the cavity with epoxy.

Note: Carefully measure the hole spacing in the fender lip and/or make a template to use as a guide to align the stud locations as the epoxy sets.

If you need pictures, I can send you some when I get home tonight.

Good Luck.

-Dick W.-

----- Original Message -----
From: Richard Koller <brvkoller@GMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Sent: Tue, 22 Mar 2022 15:37:34 -0400 (EDT)
Subject: syncro front mud guards

Hi all,
I took off the plastic front wheel well mud guards (some call them "spats")
off my syncro and of course the nuts broke off in the process. Does anyone
have any clever ideas of how to extract the remaining bolt heads from the
mud guard? These mud guards have been discontinued so I'm inquiring to see
if there may be a solution amongst always imaginative vanagon-gurus. The
bolt heads are severely embedded in the plastic and I can't see a way of
extracting them without trashing the old guards.
Thanks
Rick Koller