Try The Chassis Shop for aluminum filler caps- non vented, anodized, about $20.
Brian Trubee

Non vented? Does that mean you can not use them with a pressure cap?

Paul Lamar

They are simple filler caps that screw on and have an O  ring seal. No vent.
Brian Trubee

BTW The pressure cap is a sophisticated little device for not much money.
Two valves. One is a pressure release valve and the other a one way valve to
suck the coolant back into the pressurized system from the overflow tank.
It needs a special filler neck however. With a vent to the overflow tank.

Paul Lamar

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