On 04/10/2020 01:23, Dave Liquorice wrote:
On Sun, 4 Oct 2020 01:03:12 +0100, alan_m wrote:

Remove railings, cap stones and first course of bricks. Cover
exposed
top of wall with sheet lead that comes down the wall and over the
top
the roof covering fillet, both sides. Relay new clean bricks and
cap
stones, replace railings.

Could it be that the water penetration is where the cap stones have been
drilled through to fit the railings.?

Possibly but there are still the joints between the cap stones to
fail and let water in.


Also, there may not be a drip channel on the underside of the
overhanging lip of those slabs. All the rainwater pouring off
the edge will wick under and down the wall without a drip channel.

Window and Door external cills have a drip channel for a reason !.

Complete removal and the addition of a lead or copper flashing
right across the wall below would be the 'proper' fix.