Certainly looks like a slim, some great information here: http://www.gilletteadjustable.com/slim.html . If it is E4 then it could be a real rarity, even if the date stamp was a factory error. Can you post a picture of the underside and the inside of the head once you have cleaned it up. I am assuming you are going to clean it.
My regime is a good long in hot soapy water. Scrub with old toothbrush. Apply standard bathroom cleaner (Flash or Mr Muscle), but never bleach or de-scaler (they eat the plating). Scrub again. Peek Polish with a cotton cloth to finish. May have to repeat steps more than once