>It is still a mystery to me how the pressure can migrate from the high to
the low if it will not do it the other way.  I know that there is a higher
pressure present but .......<

Ian
This may not be so mysterious when you find the leak.  Some leaks can be
one-way.  They can act like a check valve or a diode in electrical terms.  I
had a leak in a main gear cylinder that was caused by a defective sealing
washer on the end of the center threaded rod.  Pressure in one direction
would push the washer against the mating surface, effectively sealing the
joint.  Pressure in the opposite direction however, would push the washer
away and open the leak.
Bob Jude