Two approach routes are shown for Oz Wall depending on which end of the wall is to be visited.
To gain its RH end walk past the cafe within the fort and double back on yourself at the end of a fence. Locate the third and final bench and descend the scree to pick up a path through thorn bushes to the top of Red Wall area. This is a good approach for the Red Wall routes if you bring an abseil rope and abseil onto the platfom on your left (looking out). Abseil past the big grassy ledge on Blood. To get to Oz Wall continue along the cliff top past a tricky "bad step" where Barnacle Traverse tops out. "White's Ledges" are the White Ledge referred to in Nick White's guide - they are near the cliff top which has led to some confusion. From the lower one it is possible to continue traversing and descending to the base of the pinnacle. Climb the seaward arete of the pinnacle until you can move left onto Oz Wall.
The LH side of Oz Wall is reached by going through the gate on the descent to the Great Cave of The Old Redoubt and turning left (facing out). Follow a poor cliff top path until nearly at the corner of the fort and then cut back right to descend a rocky rib towards Terminal Zawn Ledges. A tricky traverse leftwards (facing out) gains the big block which is a possible abseil point for some of the trad lines on the LHS of Oz Wall. Deep Water Soloists and those climbing on Lower Ranger Buttress (LRB) will continue down to Terminal Zawn Ledges.

It is probably not advisable to carry a rucksack at the "bad step". Perhaps leave your gear near the Red Wall abseil?