Your Vario-Elmar should work fine after you replace the mount. I have never replaced the mount on any of my Leica R lenses but have used them on a Canon and an Oly M4/3 body with excellent results. This is a common conversion on the Leica Forums using Nikon bodies. Your Leica M lenses won't work on a Nikon body. I don't even know if an adapter is made since you wouldn't be able to focus anywhere near close to ∞. But I do use all my Leica M and SM lenses on my Oly OM-D E-M5 with great results, much better than with the lenses on a M8 and I wouldn't doubt on a M9 as well.