@Summa_Brewologica I haven't. I suspect that like you, my faith wasn't there until it just finally was...but I still kind of wonder from time to time. After my initial hookup, I sprayed with Star San, Soapy Water, etc., watching, waiting to see bubbles and I never did.
A couple of weeks ago I actually turned off gas at the tank for a couple of days and just waited for the regulators to show some movement and they never did even after tap, tap, tapping.
I suspect that this is why I bought the polypropylene board very recently, along w/the stupid precut tubing. I figured with everything just so, and aligned perfectly vs. my done by hand, some tubing not quite the same length..my faith is just a little off, although the setup has yet to fail. It is still sitting off to the side, because I'd have to unhook everything and then the board itself is just a little bit bigger so it wouldn't be flush anymore.....blah, blah..
Williams Brewing did mention to me that if you suspect a leak, to remove the valve and make sure that the o-ring has some keg lube on it, or re-apply as you think necessary for periodic maintenance. I did this when I changed them out for lower PSI gauges.