You got the right idea.
I'd call that the 'pressure limiting valve' for the rear brakes.
Evidently they got no rust-prevention treatment, and are bare cast iron.
I'd scrub it with a metal wire brush to get it to bare metal, then treat is
with a rust treatment that turns it to premiered metal, then paint it.
 In situ if possible.
Scott
www.turbovans.com

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Allan Streib
Sent: Monday, December 10, 2007 8:13 PM
To: vanagon@GERRY.VANAGON.COM
Subject: badly rusted mystery part

Looking around under the front end of my '91 Vanagon GL, I noticed a
very rusted part, evidently part of the brake system, since it has
two steel brake lines connected to it.  This mystery part is mounted
on the right frame rail near the sway bar.  Is this the "pressure
regulator" that I see on a couple of the parts web sites?  The rust
is just falling off it in chunks unusual because there is not really
much rust anywhere else under the front.  Do they normally rust so
badly?

Allan