Help Needed: Can't Engage the Park Brake

In other words, I can't press the parking brake pedal down. This is a 2002
Explorer.

I normally only use the brake if I'm on an incline or such. On Friday I had
it set and it seemed to release fine. Drove around with no issues noticed.
Got home and was parked in our driveway which has a slight incline so I was
going to set the brake. Found that it was stuck solid in the up position
and I can't move it at all.

The cable seems to be okay. I can see it under the chassis and if I give it
some tension manually I can see the gear mechanism of the park brake
assembly start to move. Don't see anything else obvious such as a broken
piece or something jammed in there. The only other thing I noticed is that
there seemed to be a rubber boot around the area of the status switch which
is now deteriorated and almost completely gone. Also, the release handle
seems to operate okay.

Is there anything else I can check? Can I safely unbolt the assembly to get
a better look? Right now everything is fine and I can drive so I don't want
to get into a situation of the brake setting and not releasing. I believe
that here in Virginia this would fail the annual safety inspection.

Thanks in advance for any help or advice.

Scott