Hi Peter, having owned 9 different ajs & matchless bikes and also being a retired engineer, I make a point of fixing as many leaks as possible, this can take time though, the AMC gear selector shafts are an easy fix new seals, and then park on sidestand, swinging arm leak, many people never bother lubricating, I spent the whole weekend stopping my leak
when I awoke this morning I found that my petrol tap was leaking, drained a full tank then lapped both brass taps in with Solvol Autosol, now leak free (until the next new leak) kind regards, Ian.