Hi Mike,
the transfer case is always turning, if in neutral or drive.
If you shut off the Explorer, shift to neutral, you should
be able to spin the output flange
(with disconnected front driveshaft)
with some effort (caus of the clutch).
If there is no spinning possible, then you have an mechanical blockade
inside the BW4405.
If you could spin, i think there is an electrical problem with
the brown wire which supports the magnetic coil.
Maybe the coil is "under fire" in every condition.
The coil (from 5-12V) should close the clutch only if
the sensors registrate a spinning rear wheel.
Maybe a sensor (rear diff, 2 sensors of the TC) send wrong information?
If you treat your TC fine it last forever, so i don't think it's a mechanical problem.
Nerver heard that the clutch burned together or something.
There are some wear out parts yes, but they don't cause the TC to lock.
Did you ever changed the fluid?
If not, let the oil out and look for metal/aluminium/copper particles.
Take out the 2 sensors and look for broken magnets.
Good luck!
Wolfgang