The Mobil 1 oil filter is an excellent (if not usually overpriced) filter for the Vanagon. It performs much better than the standard Mann or Mahle. It works just fine on the Waterboxer. Oil testing in multiple vehicles has confirmed the filtering performance of the OEM filters to be lacking for extended drain intervals. 
For the price, I am using the Fram TG. I just did an oil change on my red van 4/1, trying the new Fram extra guard. After ~7,500 miles Mobil 15w-50 and the Tough Guard filter the oil still tested good. 

Dennis
 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Loren Busch
Sent: Monday, April 12, 2010 9:00 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Sale on Mobil 1 at Auto Zone

I run Mobil 1 Synthetic 15/50 in my '90 2.1L WBX.  It's time for an oil
change so stopped into the local Auto Zone to pick up the oil.  Normally
$7.49 a quart, five quarts, would normally be $37.45 (plus local sales tax,
just under 10%) but wait, on sale!!  If you buy five quarts AND an oil
filter only $29.95!!  But be prepared you HAVE to take the filte4r to get
the deal.  And I'm told the filter is a "$12.95 value".   I suggested that
they ring it up w/o the filter (not going to use their filter no how) but
no, I had to have the filter.  Okay, ring it up with the filter I said.
Then after paying (reciept shows a $20.45 discount) I tried to hand the guy
back the filter.  No way, hea really wantd me to have the filter.  So, I
saved about $7.00 on the oil and now have a filter I'll never use. I'll take
a look at it later and see what it looks like.