By all means have your Nik'mat overhauled so you can use its full range of shutter speeds.
Originally Posted by momus
But don't count on using a Leica lens on it. The Nikon F mount's register is 46.5 mm. Leica thread- and M-mount registers are, respectively, 28.8 and 27.95 mm. Leica R-mount register is 47.0 mm. There's a bare chance that an R-mount lens can be attached to a Nikon and still focus to infinity, no hope at all with Leica rangefinder lenses. Leica RF lenses can be used on Nikons, but only for closeup work. Very close up.