Good job, now the neon light test is a test we use to 1. see if it is heating without using water, and 2. it can tell us hot and cold spots in the oven cavity, but has nothing to do with a leak check. Really the only time a leak check is necessary is if you remove or replace the door. I really don't know about a down and dirty way of checking for leaks other than using a m/w leak checker, or you could just stand in front of it for 10 minutes then turn out the lights and see if you glow :) I'm sure your fine. I have never done a leak check after changing the mag tube, as there is no reason to.