Yes, whatever was used to cut the +, it was much thicker than e.g. a jeweler's saw. The appearance of the + in relation to the surrounding material also makes it look like it was done quite some time ago, but that is just speculation on my part.Maybe I missed it but I don't think it was mentioned what this actually is? This is an unfortunate old method of trying to remove screws with damaged slots. Even more unfortunate that it's probably still used now, though at least not as much. Basically someone uses some kind of saw to cut a slot in the screw, and cuts the post along with it. It's not that common, but you see this occasionally both for Conn set screws and for pivot and rod screws on any model sax.
There are two problems with it. First, it damages the post, and second, if the slot is ruined it usually means the screw is stuck, so there is even more chance of them repeating this, ruining it even more, etc.
In this case it probably didn't work in one direction so they tried another. Not that I would ever suggest this method, but in this case it looks like whatever they used to cut was too thick anyway and would never work, damage to the post or not.
Sounds like the problem is solved and the post will be replaced, but FWIW, with the ability and the right tools, it is actually possible to cut a new slot in a screw buried in a post with a damaged slot, without damage to the post. It works in most cases, in fact it nearly always does. It is extremely rare that I have to resort to alum or anything like that, which is what I do too when nothing else works. It is not really possible to do with a regular dremel, not enough precision and control (it wouldn't be surprising if that X was done with a dremel).
Of course that doesn't solve the (most likely cosmetic) issue of the X there, but that is a separate problem and depends on time, budget, availability, etc.
I have a dental micromotor as well but I still can't figure out how I could get a Conn lock screw out without the use of alumn. What size taper do you use? I've seen none in a small enough size.I do it with a dental micromotor and a tiny reversed taper bur (I prefer that type though other tiny burs are also possible).