yes.....on the socket. 
'deep thin wall' if you can.
there are two kinds of deep sockets.......those that are deep full length, and those not.
you want the full depth deep on.
a short half inch drive socket will work, but the terminal on the switch sticks out where your half inch drive ratchet would go ......
you can still make one work though.

if you are getting genuine OE German oil pressure switches ...fine.
There is no way that I'd be replacing a good high pressure switch on a 2.1 engine with an aftermarket part.
I even have half a dozen of those switches, new take-offs from German engines. 
but I sure wouldn't put an aftermarket part on where there is an original good German one, of OE grade. 

people get in trouble trying to 'replace everything' .
there is a point where it's smarter to leave things as they are.
do whatever you feel is right of course.
lol !
Scott 
glad you found 'the' leak ! 
  ----- Original Message ----- 
  From: Mark Brush 
  To: Scott Daniel - Turbovans 
  Cc: vanagon@gerry.vanagon.com 
  Sent: Wednesday, July 29, 2009 11:20 AM
  Subject: Re: Re: electric plug in engine block

  I think the switch itself is leaking.  I won't know until I buy the 24mm socket to get the thing out.  Oil pressure switches are cheap, so I might replace both.  If one's leaking, I bet the other one is not far off.

  Mark
  1990 Westy 2.1 manual

  On Tue, Jul 28, 2009 at 5:37 PM, Scott Daniel - Turbovans <scottdaniel@turbovans.com> wrote:

    if there is a metal sealing ring between the oil pressure switch and the engine block ........
    it could be leaking there, and tightening the op switch or putting in a new sealing metal ring, if it uses that system, might help.

    Hi mark 91 westy,
    Sometimes it's hard to tell where they are actually leaking from.....
    whether from the wire connection area, the 'top' of the op switch, or from where it screws into the engine.
    try spraying white talcum or baby powder onto  the area, and see if that makes 'the' leak stand out.

    oil pressure switches can leak, but I can't think of the last one I replace for that reason, fwiw.

    some oil pressure switches are tapered at the threads, and don't use a sealing washer.
    some are not tapered, and do use a sealing washer.
    be sure of  which kind you are working on.
    if it's an aftermarket american one or something ..........I wouldn't want it on my vanagon, that's for sure.

    Scott

    ----- Original Message ----- From: "Mark Brush" <mbrush@GMAIL.COM>
    To: <vanagon@GERRY.VANAGON.COM>

    Sent: Monday, July 27, 2009 7:18 PM
    Subject: Re: electric plug in engine block

      Yep - that's where the leak was coming from - the oil pressure switch.  It
      was leaking oil badly enough that it was picking up some water that I
      spilled on the block during the coolant drain and fill extravaganza - so it
      looked like water.  It's oil upon closer investigation.

      So - from what I can tell - that thing has an o-ring - or maybe I'm better
      off replacing the whole switch (maybe it's cracked or something) - any
      thoughts on replacing the sealer (o-ring) vs. replacing the whole switch?

      eternally grateful,

      Mark
      1990 Westy 2.1

      On Sun, Jul 26, 2009 at 10:36 PM, Mark Brush <mbrush@gmail.com> wrote:

        Yeah, that's the one.  Could mine be leaking coolant/water?  The leak must
        be coming from somewhere else...

        On Sun, Jul 26, 2009 at 10:00 PM, Scott Daniel - Turbovans <
        scottdaniel@turbovans.com> wrote:

          Sounds like you are referring to the oil pressure switch there,
          between the push rod tubes .
          that one ?

          Scott
          ----- Original Message ----- From: "Mark Brush" <mbrush@GMAIL.COM>
          To: <vanagon@GERRY.VANAGON.COM>
          Sent: Sunday, July 26, 2009 5:52 PM
          Subject: electric plug in engine block

           Hi All -

            What's that electric plug going into the engine block?  It's near the
            coolant drain plug on the left head.  Mine's leaking and I can't find any
            info on it in the Bentley - and I haven't found a posting on the
            listserve
            yet.

            I have a 1990 Westy 2.1 with a few leaks (btw - I just used the bong
            method
            for filling with coolant and it worked great!)