fx impact leaking around front air gauge, any fix help?

These stupid gauges are poop. Few are accurate and they all insist on using the BSPP thread form. I hate BSP threads. Only the Brits use it. They use a 55 degree thread form like Whitworth threads rather than the modern standard 60 degree for metric and US national thread forms and specifically, the BSPP standard seals at the base not the thread itself. This needs a sealing flat washer at the bottom of the hole and the finish of the hole bottom must be perfectly smooth and scratch free as well as the gauge thread base in order to seal. This washer can be nylon or fiber, not rubber. I prefer fiber as it doesn't flow under pressure and they seem to seal better at these high pressures. If you want to inspect the sealing surfaces of the gauge hole or inspect/change the sealing washer, you will have to drain the tank of course.
 
no need to degas to tighten the gauges just tighten a little at a time and check with some soapy water and a Q tip around the threads for bubbles

That's the easiest fix indeed. :) 

If it doesn't work, unscrew the bottle until it starts to hiss, remove the gauge. Check for contamination and inspect the x-ring or o-ring (for newer models, older ones might have a delrin washer)

In case of an x-ring, don't overtighten it or the gauge won't indicate the pressure anymore (because the rubber will seal the entry hole of the gauge.)

When this doesn't work, you can always apply some teflon tape around the threads to make it seal.
 
I'd be careful. I twisted a gauge off on my Wildcat while trying to install in the bleed port. "Before" I knew about the delrin washer. I was using a Huma gauge, and the base where the threads are is brass, and rather thin, because of the hole in the middle. Took very little effort, just twisted off. Had to use an easy out to get the broke piece out. If your doing this under pressure, and it snaps, you might get a face full of gauge.