easy;
Try cleaning thoroughly with brake cleaner/wire brush then try patching with $4 tube of JB weld.

harder;
Remove valve cover, rockers, push rod (of the offending tube) then rip out the push rod tube with vice grips, cutters.  Replace with collapsable style;
http://www.van-cafe.com/home/van/page_561_267/expandable_push_rod_tubes___see_description.html

hardest;
remove head, replace with regular pushrod tube

---------- Original Message ----------------------------------
From:         John Meeks <vanagon@GMAIL.COM>
Reply-To:     John Meeks <vanagon@GMAIL.COM>
Date:          Fri, 25 Jun 2010 19:12:17 -0400

>I'm no BP but I've been leaving 6" poodles if oil wherever I park.
>I have tracked it's source to a tiny hole in the case side of a push rod
>tube right
>on the outside of one of those accordion  ridges.
>http://picasaweb.google.com/vanagon/SaltbeltRustyParts#5486847990506798578
>
><http://picasaweb.google.com/vanagon/SaltbeltRustyParts#5486847990506798578>I
>don't want to pull the head to replace the tube so... Does anyone have any
>idea what
>I could use to repair this ~3/32" hole
>
>John Meeks
>'91 Multivan
>Northern Michigan
>
>Vanagon Rescue Squad
>www.vanagonauts.com
>