Shortly after running through about a foot deep puddle in the backcountry, I
noticed unmuffled engine noise and eventually traced it to a missing
component in the exhaust manifold.  See photo here:
http://www.takingflight.net/images/manifold.jpg

This is a Rabbit/Golf engine, around 1986, in a converted 1982 Vanagon.

What is the missing piece?

Thanks,

Paul