Yes, in fact this may have been the repair that was done before as one of the screws is a bit longer than the rest. What became of the nut, I don't know. Unfortunately I don't have a tap large enough to fabricate a new nut (yet). I've ordered a set though so I should have this sorted out soon.
While waiting for the tap and die set I went about replacing the crystal for the case lid. The original crystal was chipped and didn't survive being pushed out during the cleaning process. I The replacement is a 33.6x2.0mm flat mineral crystal. The sighting line runs from 12 to 6 on the crystal. In order to replace this line I first etched the crystal using a bit of etching paste I picked up online. The dimensions of the line were marked off with a bit of packing tape and the paste applied to area between each piece (of tape).
After about five minutes the etching paste was removed with a dampened cloth and the tape removed. I near perfect line running the diameter of the crystal remained. This was filled with a bit of black enamel and left to cure.
Twenty-four hours later the excess black enamel was removed using a felt pad and the Dremel tool. What remains is a very fine black sighting line.
Now, I somehow managed to misplace one of the mounting screws for the crystal so I'll need to turn a replacement in the lathe. This is also an m2.0 thread so it will have to wait until my tools arrive.