Ko.Fe dont think your old case will fit M240 series. screen dimensions and button layout is different than in M8/9/M-E.
M240 battery is lot better than those old models, although if bought new, still quite pricey (like older Leica brand batteries).
Leica jpeg engine is not too far apart from older CCD models to modern CMOS models.
I got my little used M240 recently for 2300eur, prices have dropped quite nicely. its still my most expensive camera to date, and took long time to commit purchase.