>If any one has a spare (034 121 119) could you
  >tell me what the I.D and thickness is?  Also if there are any
  >painted coloured bands on it.  (This may help indicated o-ring
  >material, buna or nitrile).

Mike,

        I'm looking at a used o-ring from my '91. it measures 6 cm. ID and just
under 3 mm thick
It is probably 3 mm when new. It bevels down to 2 mm on the inside diameter,
but this may be a result of 12 years at 7 ft lbs compression and thermal
cycling.

No visible markings on it.

It goes on top of the thermostat.

Regards,

John Meeks
Top of Lower Michigan
91 Westfalia MultiVan

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