main issues here "MONEY AND STOPPING LEAK "
If you was to just slap on some flashing tape you would have a problem sealing it with the brickwork crumbling and in the state it looks .
mix up some sand and cement put some pva on the wall and fill all the voids in the brick work . you could...
i would not dot and dab a 9inch wall as Solid brick walls can be penetrated by rain . i would batten and board and i would use tri iso 10 insulation it is 30 mil and equivalent to 210 mil of rock wool ..
i found this link for you
http://www.just-insulation.com/super10.html
with the bad weather we have had frost and snow etc it causes a lot of damage to roofs if there is nails in the valley it will only be to hold the lead or zinc down and then overlapped . if you do go up on the roof remember water does run uphill beleive it or not :lol:
it is not the done thing but you could move the pantile over 6 inch and it would slot into a different groove . If there is a verge on the other side this would move the problem over to there idealy it would be great if you had a valley there . i would ask for a different BCO to come out some...