LensBrew

Sony's mount system lets use FF lenses on APS-C bodies and APS-C lenses on FF bodies, and this is now being copied by other brands.
The lens will work perfectly fine, but you'll need to go to APS-C mode (super 35) to remove the "vignetting" and this will make the lens 15-30mm. Therefore, in addition to changes in the focal length, your image will have approximately 24 Mpixel resolution.

I would recommend to identify what specs your current bodies don't have, and how much it will better your work. Remember the law of diminishing return. The other reason for upgrading is if the bodies are showing their age in your workflow and images.

Primes are my favorite and I do prefer them. The answer would depend on the shot that you missed and what lens do you feel would have done the job. 35mm GM is my favorite and capture amazing angles. I would recommend any of the 24mm f/1.4 GM. It's newer than the Zeiss, faster, lighter, a very great lens and only $50 more expensive.

Not possible to know without opening it physically and doing a thorough inspection. But I suspect the culprit to be the lens motor or the gear coupling for that motor. Usually some foreign object might got in there, or a piece was diffracted and only recently showed up as an issue.
I don't believe anyone "repairs", in the sense of fixing a part and reusing it. But It can definitely be replaced, and with a bit of internal cleanup the camera should be as good as new.
But until then, I recommend you do not operate it to avoid exacerbating the problem or creating new ones.

Hey Trek, I had that discussion with some of the pro photographers from other outlets. They actually would be proud you shot a lot. the points I concluded from our conversation is fairly simple. Sports is very fast, and the moments flee in milliseconds. Out of a 100 you get 1 good shot, out of a 1000 you get 10. In the end, the game would have that 1 or 2 moments that you're either lucky to capture or unlucky to miss. And the final element to affect the image is the result. If you got the shot of the best moment, but the team loses, it becomes a normal shot. Therefore, Luck play a big role is sports, and mass shooting becomes necessary after great skills to increase the luck factor. In the end, memory is cheaper now and no restrictions apply.
You might be thinking of post work, and my advice is to review the images during the game when the play is paused for any reason. I have a custom button to star images as I review them, and usually I have a sense of which set of shots would have the best shot and instantly rate it.
This is image from the last women basketball game I shot and was the big moment shot (in my humble opinion). The coach rarely shows his emotions, but not during this game, and especially that this is the first time they beat Louisville since 1995. Only the last sentence (information) makes the image a lot more meaningful.