Sorry, bad news. Brockley Section Z consists of about 600 unmarked common graves behind only 2 or 3 rows of 100 or so monuments on private graves along the edge facing Section X. The unmarked area is covered with long grass and brambles making it impossible to see headstones if, indeed, there are any. However, unlike elsewhere in the cemetery, the growth doesn't mostly reach head height in summer.
This photograph looks across from near the corner with Section X and the road. Your browser may support using the mouse to pan around (shift/wheel) or zoom (control/wheel). On the middle right it's just possible to make out a path which arches across the area towards Ladywell Section G. They keep this mown, enabling you to get a closer view of ... loads of long grass and brambles. I'm afraid I don't have a map of the plot layout to locate any particular grave.