I asked for some help with this one (few days ago) on RGP.

The following was posted by a fellow RGP'er Kerry:

"U5 Pin 15 is driven by inverter Z26.  Z26 pin 13 should be high (+5V)
normally and go to near 0V when the slam switch is closed.  Z26 pin 12
should be opposite (near 0V normally and go to +5V when slam switch
closed).  Bottom line... make sure U5 PA7 (pin 15) is near 0V (I would
guess it should be about 0.2V). "

My pin 13 is low 0.01v and pin 12 is 5.014v

Slam mod is definately done (removed old one and redid again).

I replaced Z26 this morning, no difference.  Assuming the above is correct, something weird going on (apart from me miscounting pins)