Huh, my neighbor has a white TDI Jetta with exhaust pipe extension that
turns down.  I always thought it looked tacky but now realize it may have
some real functional value.

I guess the best thing is identify the residue.  If its soot, put 3 coats of
wax on the back on the van so the spots wipe off easily.

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
James
Sent: Friday, August 22, 2014 12:10 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Advice about black oil on back of diesel Vanagon

...

One thing that helped was an exhaust extension that was turned down, so the
exhaust was more likely to hit the ground or be carried away from the
vehicle by the air stream under it. ...