Mine was metal. Yours might be copper. It's behind the push rod cover. As soon as you take the cover off, you'll see it. The area shown in the picture is where the rear-most end of the tube threads into the block. In the photo I have removed the fitting the tube threads into but the fitting itself was packed full of crud, too. I don't know the history of your engine, but mine sat for many years. I had to eliminate all the suspects from the rockers to that particular fitting and this included the overflow tube that loops over the rocker arm assembly, the drilled-out head bolt next to that tube, the passage in the block that leads down behind the push rod cover, the tube behind the push rod cover, and finally, the fitting I showed in the picture. There is a threaded plug on the passenger side of the head that you can pull while the engine is running and see if there is any oil coming out. If so, you should be good. In fact, that's the first thing I'd do before taking stuff apart.
