The 12mm did not come from the factory. That is an ISO, not DIN spec although there are some places the smaller head is required. 

Unless the engine is running oil loss will be minuscule. This port is right behind the center cam bearing. 

Dennis 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Rocket J Squirrel
Sent: Sunday, May 29, 2011 12:01 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Yeppers -- failed oil pressure switch alright.

(1981.9L) Got the tin off the bottom of the left head. Three 13mm and one 12mm? Who designs such things?

The switch reads open to frame with the engine off, so it's a goner.
Found the fossilized remains of what appears to be an ancient Pre-Columbian rubber boot on the switch. After than crumbled off, the the brass push-on connectors had nice green verdigris.

I gotta do something about this.

When I pull the switch, will there be much engine oil loss?

--
Rocky J Squirrel