Cape of Good Hope 1855 4d Deep Blue Stroke in First "E" etc

1855 4d deep blue triangular, variety STROKE IN FIRST "E" of "PENCE" (SG 6var). VF/U with crisp triangular canceller. Full margined, a very deep shade with remarkable show through (oxidation?) of impression to reverse. An elusive constant plate flaw. Expertised: Ferchenbauer. See additional image.