Yes I am doing similar. I dig it all out, let dry, repoint, and then fill with 49mm clean stone. On the deepest face I have perf drainage at 3 levels which joins to pipes down the sides. Much be better than clay!!!Looking at your photo's it does look like you need a 1 metre deep french drain putting in on the sides into the hillside. I have one on my farmhouse as one wall is 1 metre below soil level. It has clean limestone as the french drain fill and drain pipe at the base. Large welsh slate sheets seperate the french drain limestone from the stone of the house. It works very well and the walls are dry despite being in very wet Lancashire.