In reply to FesteringSore:
Solid wall or cavity wall?
It may be due to quantity of rain/damp weather we had soaking through brick rather than the flashing itself, or a leak further up the wall. Old cavities were narrow and normally full of 'snot' (dropped mortar) or broken bricks, these bridge the cavity and the water tracks across. So don't necessary assume it is the flashing as this is closest to your leak.
Some leaks can be hard/expensive to find. Silliconing or lead seal can make things worse, as people often can seal around all the bits where the water is meant to flow out and make the problem worse.
Good luck with it.