>   I'm trying to find out if the leak in the gauge casing signifies an
 >   explosive potential, a point on which I'm still not clear.
If your gauge is leaking air, you are indeed risking a situation where some 
point in time that gauge will explode, first blowing glass all over the 
place, and since it's a high pressure line, you will empty your air supply 
very rapidly.
If any water is coming back into the gauge, you are also risking a problem of 
corrosion from the reverse direction.  If your diving in sea water, you have 
also accelerated this problem.
Get it replaced before your next dive trip.
Beery
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