The ejector rod coming unscrewed is a common N frame Smith revolver problem. I have 4 N frame smiths and I have had every one have the ejector rod unscrew after the gun is fired a few hundred rounds. Its even happened on my 2002 629 mountain gun, so its not just a problem on the older guns. Tighten it carefully with two empty cases in the cylinder, so you don't bend the rod or the locator pins on the star. It will come unscrewed again.
Here is what you need to do to fix the problem remove the cylinder and yoke, remove the cylinder and unscrew the ejector rod. The star, ejector rod, plunger, plunger spring, ejector spring etc will all come apart. Carefully clean theejector rod and extractor star threads to remove all the oil and use red locktite on the threads, not too much, reassemble all the cylinder parts and tighten the ejector rod extractor rod thread and let it sit before reassembling to the yoke and frame.
So far I have not had an ejector rod unscrew on a gun I locktited in this manner.