Wait, you're stopping there? What about the power supply? Tear it down too, or at least test it's outputs. Thanks for this trip down memory lane. =)

Seems to have worked. Next time I will reads all the instructions first. One more thing, "Test pump to its highest rated pressure and listen for leaks. If you can hear leaks from the gauge, tighten it." I don't have any way of testing the highest psi. I pumped to my tires highest psi and waited about 2 minutes and no change, so I'm calling this a successful repair. Thank you very much Lezyne, and specifically Colton Arbuckle for your help. =)

Removing the old face plate and gauge internals was a blast. =) However, Step#6 of the guide above says;

"Allow at least 30 minutes for the thread locker to set.

Test pump to its highest rated pressure and listen for leaks. If you can hear leaks from the gauge, tighten it."

The guide that came with the replacement parts says to "Let the Locktite cure for 1 day before pumping."

I think I used plenty of Locktite, I tightened the gauge and backed it off 1/4 turn to face the handle, I'm gonna let it cure overnight and hope for the best.