Update:
Onsite repair came the other day and now my iMac is tilting again. But, for how long? The failure was indeed the iMac’s stand tilt mechanism in which one of the two springs broke through the plastic washer-like part that holds down one side of the spring. The tilt mechanism has two of these plastic washer-like parts; one per spring.
The contracted tech who came to my home was fantastic! He was pretty knowledgable, friendly and except for having to run out to a local hardware store to buy a #4 Torx bit, everything went smoothly on the first try in a couple of hours. The #4 Torx bit was necessary to remove the wireless and bluetooth antenna’s from my old iMac shell and put them on the new shell. “Shell?” you say! Yes, because at least for my repair instance, Apple Support had sent the tech’s company a brand new iMac 27in aluminum back shell that was empty, except for the tilt mechanism that was included and attached to the shell sans actual stand.
So the tech had to remove everything out my iMac, including the 3 antenna blocks screwed to the shell around the edges at three places, and the actual stand. I took a lot of pictures, asked a few questions and was given some nice tips during the repair and in the future when my Apple Care has expired and if the tilt mechanism fails, or for that matter anything else inside my iMac fails or I would like to upgrade, I now have my illustrated bread crumb guide to get me in and out of that dark nether region Apple is trying to deter everyone from going by virtue of their design philosophy.
Since I was last here on this thread, there are quite a few more users reporting the same failure. I hope that all users get a satisfactory fix and I ultimately I hope that Apple engineering comes up with a permanent solution to this failure and even perhaps retrofits all those that have reported this failure with that permanent solution. I wonder what the likelihood of that last suggestion is? Hmmmm…