Later GT (not V8) cylinder showing the locating peg further away from the fluid port ...
... than the roadster, early GT and V8:
Vee's offside cylinder with the location roll-pin eroded away
Bee's right-hand cylinder which had just started leaking during a service. This image makes the outside look very rough and rusty, but in fact it is shiny metal, just a rough casting.
Right-hand end (the lower end when installed) containing rusty fluid in the boot and the bore with roughness, the other end was fine.
However with the pistons removed and the bore cleaned it was largely polished and shiny, but with several very localised areas that had been significantly eroded away, two of them arrowed here (the oval area between them is the bleed port). Was this very poor casting that the boring process failed to clear? Or porous metal in that area that rusted much quicker than the surrounding metal? They are both at the lowest part of the bore when fitted, so it probably is something to do with water in the fluid.
Something else I noticed was how easy the pistons pushed back into the bore, even with dry seals. I can remember in the past when I've changed seals having a helluva job getting them back in even with hydraulic fluid as a lubricant, because the seals stuck out so far. These stick out hardly any further than the pistons, and when you take the clearance between piston and bore into account will hardly be pressing on the bore at all.