After removing my CRT and cleaning around the neck, I could clearly make out the crack you see in the photo I've attached to this thread. After closely examining photo's made prior to this, it appears that this crack was present all along and probably even before I brought the set home. The very dim picture along with this crack around the neck is enough to qualify this as a "bad" CRT, in my opinion.
If I am to bother trying to repair this set as intended, I will first have to find a suitable replacement 17LP4 ( or 17VP4) CRT. I'm not sure how many of these are around or what one will cost me, but if nothing turns up, I'm afraid this will force my Zenith into retirement as nothing more than an interesting piece of furniture.