Power Steering leak??

My sons 91' Explorer 4x4 Eddie Bauer has a power steering leak, it doesn't seem to be coming from the pump itself. But there is a noticeable leak just above the pitman arm, I believe this is the Power Steering gearbox?? How tough of a job is it to fix and do I need to replace the gearbox or just seals? Also anybody know how much the gearbox runs? Any help would be greatly appreciated.
 
thanks,
Fordhog43

There is an old fashioned way to remove the lower seal in the sector box, but the hard part is removing the pitman arm.  You must have a puller for it.  Next, remove the snap ring that holds the seals and start the engine.  The pressure will blow the seal out.  Question is, can you still get a kit to replace the seals?  It might be easier to just replace the gearbox, again, the hard part is to remove the pitman arm.