Without opening the safes (intentional plural) I would guestimate that I likely have well over half a dozen Zeiss scopes and I have never had any issue with any Zeiss product (I also own a couple pairs of Zeiss binoculars as well) in 30 years of hunting. These are extremely well engineered and assembled products, especially the German ones, and especially those made in Germany before re-unification, i.e. the ones marked West Germany. Yes "modern" glass is better, but in many cases it takes laboratory equipment to measure the difference...
Reading this post, a few thoughts come to mind...
1) Your original post says: "I remounted it to my .375, fired a few shots to rezero and put it away. That fall I got it out to get ready for a bear hunt and the scope was doing the exact same thing as before I sent it off." This would lead someone to think that you re-mounted the scope and re-zeroed it without any issue, and that somehow during that period in the safe something mysteriously happened. One thing I can think of, and it happened to me with two Swarovski scopes, would be the lubricant of the zoom ring hardening enough to prevent rotation after years of storage. On these Swarovski, I managed to turn the zoom ring with great effort a few times, and within minutes the issue was solved. The friction likely heated up and softened the hardened grease. I later discovered that I was the guilty party when I wiped the scopes with the same silicon cloth I used on the rifles, and its oils seeped into and reacted with the zoom ring internal lubricant. My bad...
2) Looking at your pictures, I can think of something much more likely. On this model of Zeiss scope the zoom ring actually forms the bell of the rear ocular and nothing prevents it from contacting the rear base ring. If the scope slides forward under recoil (you mention a .375), the zoom ring can actually become locked in place by contacting the rear base ring. I have actually seen this on a friend's similar scope. In my friend's case, the solution was as simple as loosening the rings, moving the scope back 1/4" to clear the rear base ring, de-grease the rings and tighten the screws at 30 inch/lbs with a torque wrench (many scopes rings & bases screws are not torqued at the proper value, including some mounted by professional gunsmiths). That fixed the issue for good.
3) A scope that is sliding forward in its rings will not hold zero. The sliding will be imperceptible to the human eye, but enough to move the point of impact of few inches at a time, and the shooter will likely not realize it until, with a scope like yours, the rear base ring locks the zoom ring in position; or with other scope designs, the shooter may never notice it at all and the scope will come to rest with the rear ocular bell shoulder contacting the rear base ring, and all of a sudden the shifting zero problem will mysteriously disappear - I have seen that with my own .416 Rigby with a Schmidt & Bender in Alaska Arms rings, despite proper torquing. That is especially true with older, heavier scopes like yours, and my S&B 1 1/4-4 x 20 with 30 mm tube.
In summary, I have seen #1 explaining a locked zoom ring; and #2 & 3 explaining both a shifting zero and a locked zoom ring. Is this your case? Only you can say...
As to blaming Zeiss for voiding a Return Authorization after a year without actual return ... it seems we all agree on this one...
PS: As to back up, that is why I take two scoped rifles to Africa, not just two scopes. Have you ever seen base screws break or a stock split?
OT, NO fore end stop on the Caldwell rest.
