it is a square section ring, not a round section. I got one from dealership a few years ago. i agree, round can become square, but in this case it starts out square.

alistair

On 2012-11-01, at 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.