The cylinder base o-ring is at least as old as the head gasket that failed causing you to go there in the first place. If no sign of ever been overheated and you feel lucky leave them in place.  Otherwise, pull the pistons so you can also check the rings, The pistons should really be placed back into the cylinders from the top which means you need to address the carbon ring.  If you don't replace the rings have the oil tested after about 1,000 miles to make sure no antifreeze is getting by. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of J Stewart
Sent: Thursday, February 20, 2014 10:05 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Changing the Black O Ring On a Cylnder Sleeve...

I'm guessing impossible without pulling the sleeve all the off the piston. I tried it on my spare engine, on #2 (#1 sleeve is already off) and by the time I pulled the sleeve out far enough the lowest ring had popped out. I tried this before doing on my engine that is still in the van with the right head off. I've heard differing opinions about the need to replace that O ring. Thoughts? Personal experiences? I'd love to hear them! Thanks!!

Jeff Stewart