Hi,
In reply to ChrisX.
There is tendency for this to happen and I think that it is the result of wear in the thread in the aluminium case. Over the years the hammering that this adjuster must get will inevitably take a toll. Even with the 'top hat' fitted they can still leak.
I am in the process of solving the same problem and will perhaps find some Dowty washers and use some PTFE as well.
Dave.
I wrapped a little ptfe tape around thread, which seems to have solved it. I have ordered some Dowty washers as well.
Chris