@c-anon, wow, I don’t know if I would try this on an 24-70! I think that’s a more complex lens to work with (being that it has full time manual focus and there’s a focus clutch in there…), but again, I wouldn’t know at all. You’re going to have to proceed at your own risk here, as I did with my lens.
I don’t really know where or even if your particular lens is going to need lubrication as it’s probably going to be different. My lens would stick whether it was autofocused or manually focused, so I ruled out the autofocus pretty early on, and I wasn’t sure it was a lubrication issue until I was pretty far into the process.
I had to look at it for a while to figure it out, but for mine, there was a tube of the lens that telescoped into another tube and moved back and forth to focus. For my lens, this was plastic on plastic and wasn’t moving freely… so I coated the whole thing in a very very thin layer of lithium grease. Then it moved freely after that.
I think you’re just going to have to be very careful going in, look at it with a critical eye, and solve the puzzle. I don’t know if it’s a lubrication issue for you or not as I’m not the one looking at and playing with the lens.
For me on my 18-200, I kept tearing it down testing the focus after each layer because I didn’t know if the problem was really the focus or some other part of the lens—perhaps it was a loose screw or something. I got all the way down to the focus mechanism (inside the lens) and after playing with it and moving the part back and forth as the lens would have if it were assembled, I determined that I was holding the part that was the problem. So I partially took apart the focus mechanism, greased the whole tube, and started putting it back together. I want to say I kept checking the lens for focus problems as I was putting it back together to ensure that I had solved the problem, but I think my main concern was just getting it back in one piece at that point!
That said, be very careful, keep track of all of your screws coming out, take pictures, make marks on parts that separate so you know the proper orientation going back in, and see if you can’t find a teardown video on the internet to help you get it all back into one piece.
Oh, and if anything looks like it has hot glue over the screw head or there are weird oblong washers or spacers around the screws, do not take that apart if at all possible.
Good luck!
—Logan