[Pilotdave]

Thanks for all the added ideas and information. I believe that I have an original inner nut - the threads are indeed sharp and rather fine and the nut has some 'heft' to it. I have cleaned up two spots in the threads in the housing and now the nut threads in nearly all the way to the bottom of those threads. (I do have the higher quality steel tool - certainly a better option than a cast tool.) I didn't try assembling the gauge with a gasket omitted to check tolerance - didn't see that post until after trying what follows!

I decided to reinstall the gauge and refill the tank to see if we'd solved the problem. So far, there are no leaks. I am going to cycle through a few tank fillings before I declare final victory, but the initial results are favorable!

Thanks again to all of you who contributed to this thread....hopefully you will never see another thread from me on this topic!!

Dave