To maybe clear up something, the spool is inside the fittings. You have to remove the hose to see it. It is what allows the SPG to rotate and still seal the hose. As in the photo above, there are 2 orings that do the sealing, it's not uncommon for them to get old and start leaking. The good news is, even if they fail, it will not drain your tank fast so no worries there and the fix is inexpensive and easy. Not saying you should not abort the dive if it fails but it's also not a big deal.
You might find this interesting
You might find this interesting
