Yup... some have a rubber washer/grommet/gasket/o-ring/whateveryouwanttocallit at the flange... mine does but my radiator isn't stock. You can get replacements at just about any parts house; At least, you can in my area.
I think 2F needs a new seal on his.... you may replace just the seal or just go and get the plug, the difference in price is nothing.
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