The rear brake caliper bolt (bottom) is obstructed by the rear shock. I had a allen wrench socket, which won't fit in the tight space with the wrench attached. I bet a regular allen wrench would fit much better (or cut off a little of the allen socket).
From hayaku. http://www.xoutpost.com/showarticle-196.html
"Step 29.......Remove the guide bolt dust cap (just the top)..........
.....
You will not be able to fit a wrench and socket into the lower guide bolt to remove it because the shock body is in the way...."
I was able to put the hex 7mm socket into the bolt and use an open end small wrench to turn the bolt by turning the exposed allen socket.
Other than that, pretty easy.