The F-4F was a lighter F-4E, a fuel tank was deleted as well as AIM-7 provision, and no in flight refueling receptacle.
The modernization delivered AIM-120 provision as well as new avionics, including an APG-65 radar. I'm guessing here but could in flight refueling capability have been added in as well, given the different circumstances the Luftwaffe now operate in, no longer being confined to Central Europe?
As this was not an as built receptacle, could it be that this modification is visible at all times?
My sources don't mention anything about deletion of the air to air refuelling. In fact, I have a 1984 vintage pic of onetaken form a KC-135. Granted, it is very hard to tell the difference between an F-4E and -F from above...
As for if the modification is visable at all times.. I would wager that if the recepticle was to stay open, they probably would not have even bothered to install doors on it.
Whoopsie, just had a look at a cutaway drawing of an RF-4C, to see how the airforce AAR recepticle is set up. Ignore the comment above about the doors. I did check other photos of F-4F's in the database, and it seems the recepticle is closed in flight. The cutaway I was using before was that of an F-4M. Not too helpful for this question.