Was giving my 91 Legacy the look over under the hood tonight, noticed dried coolant trails down the end of the radiator stemming from the air bleeder plug. Now this radiator is less than a year old, was disappointed to pull out the bleeder plug to find the plastic POS was cracked bigtime and the rubber washer falling apart. Ran down to the parts store, could find anything to use of same thread, so ran over to harware store and among everything else in Metric hardware section was bin of Oil Drain plugs, Metal with washers. M12 x 1.25 was the size for mine.

This fix worked me, too. HOWEVER! Be careful, the new bolt will get HOT since it's metal.