Most parts stores should have something.
If you can't find one... get some gasket material and make one.
In either case... Use a THIN layer of RTV silicone on both sides.
Make sure all the metal is very clean and dry. Let the RTV set over night if possible before filling the system.
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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave (It's also at the top of every forum page...)
