I was starting to flush and refill the radiator on my 1997 Ranger (which has been sitting idle for awhile), and when I got down to open the petcock drain, I couldn't get the plastic nut to move. Upon closer inspection, I realized there wasn't a nut left to open...it had been chewed on by squirrels until there was almost nothing left. My question is, can I replace the petcock drain, or is it built into the radiator?

 

Yes that plastic plug can be replaced.