There is an oring you cant see on firebolts that cause this leak
the bit where it screws together in the middle there is an oring sometimes you just need to check the bolt is screwed together properly otherwise put it in warm water to break loctitre down then unscrew check,clean and reseal using loctite or ptfe tape
http://www.zdspb.com/tech/mguide/ion/maintenance_bolt.html
Scroll down to firebolt it is the oring marked 11/70
hope that helps
the bit where it screws together in the middle there is an oring sometimes you just need to check the bolt is screwed together properly otherwise put it in warm water to break loctitre down then unscrew check,clean and reseal using loctite or ptfe tape
http://www.zdspb.com/tech/mguide/ion/maintenance_bolt.html
Scroll down to firebolt it is the oring marked 11/70
hope that helps