if a person seals that spot with The Right Stuff..
no o-ring is even needed.
  Just clean things very well to bare plastic and rubber..
put it back together with a high quality black sealant.

I use Toyota's black sealanta lot too.
Never fails to see perfectly. Comes apart years later just fine.

scott
turbovans

On 11/1/2012 9:21 AM, Mike B wrote:
> Many VW components use normal round-shaped o-rings.  They start out
> round in cross-section, but get compressed and flattened into the
> squared groove upon assembly.  When they've been in service for many
> years, they harden and take a set into this square shape, and it's only
> a matter of time before they start leaking, as they no longer are the
> same size or shape.  You may be able to get it to seal up again by
> adding some sealant and re-assembling the parts, but it really just
> needs a new o-ring.
>
> Mike B.
>
> On 11/1/2012 11:41 AM, JRodgers wrote:
>> There is a gasket that seals the valve to the body of the heater. The
>> gasket is not like an "O"ring - round in cross section, but is instead
>> square in cross section. It fits nicely into a square shaped groove.
>