Land Rover Repair: ZF 4hp22 transmission 1989 range rover classic, range rover classic, electronic controls

Question
I have a customer coming in that was experiencing a no shift into 4th the other morning when it was cold.  He had to feather the accelerator to get it to shift then it stopped and shifted fine.  The other day at the grocery he had no reverse, when he got home and since then he did.  Any ideas what it could be?

Answer
Whatever it is, is inside the gearbox.  The fluid is full and normal looking, right?  You know to check fluid level cold, too, right?  Beyond that, there are no electronic controls, and no adjustments.  We would pull the box and send it to ZF for overhaul.