Exactly guys!
Sorry no key for the C/12D itself, but by using the key from a similar Revi 16B drawing (plus logic), I make it:
1. Tinted glass retaining screw, 2. Tinted glass plate, 3. Ring sight (with cross hairs), 5. Reflector plate retaining screw, 6. Reflector plate, 8. Bead sight, 9. Bead sight adjustment screws, 13. Objective lenses, 14. Crash padding, 15. Sighting image lens, 16. Light focus lens(?), 17. Bulb housing cover, 18. Light bulb, 19. Dimmer switch, 20. Horizontal adjustment screw, 22. Light bulb housing, 27. Dimmer rheostat, 28. Base plate, 29. Tinted glass pivot mount, 30. Tinted glass protective plate(?)
If anyone can clarify nos.16 and 30 better, or notices any mistakes, please say!
Some more random pics (incl. mount) from same book, plus 2 sketches from M.Hobby publication 'Messerschmitt Bf.109' by B.Pomahab: