I work with a fair amount of commercial and industrial equipment and I often see a very obvious and very effective solution.
Silicone. Pick your favorite color or brand! Works every time!
For high pressures two part epoxies do super too!
I have used JB weld on hydraulic fittings up to 5000 PSI peak pressure and never had a leak yet and some of those fitting are on constant use and have never leaked a drop in years. Plus if you do need to take a fitting apart it will let go and cleanup with a simple die grinder wire brush.