The Vanagon head gasket design is not anything like the Subaru or Jeep which both are conventional gasket design. Any solids based sealer may work. Any sealer may also clog up any marginal radiator or heater core. 

If the gasket is failing from corrosion debris squeezing it at some point it will tear and cause a massive loss and a tow home. 

Dennis
  

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Dan N
Sent: Saturday, December 19, 2015 8:18 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Dreaded water jacket head gasket leak strikes

for now you may try this Subaru coolant conditioner

http://www.amazon.com/Subaru-SOA635071-Coolant-System-Conditioner/dp/B00IGZP2UE/ref=sr_1_1?ie=UTF8&qid=1450574144&sr=8-1&keywords=subaru+coolant+conditioner

it's working well on my son's Jeep.. loss of coolant but no leak (internal
leak)