It would be interesting to see if what you are seeing as fog in the leader is actually silver. You could use Farmer's reducer and refixing on a portion of the leader and see whether the fog goes away. Treat half the leader with the reducer and leave the other portion untouched. So years ago Ilford had a system for reversing their films which used a permanganate bleach. Some people were experiencing what they thought was fog but which was actually manganese dioxide precipitaated in the emulsion. This was caused by an improperly compounded bleach. The bleach must be sufficiently acidic to prevent precipitation of either manganese dioxide or chromium oxide in the emulsion due to carryover of developer. Do you use a rinse between the first developer and the bleach?
Here are the instructions for Ilford's process http://www.ilfordphoto.com/Webfiles/20061291034093.pdf