Sounds like your NSS is fine and the tranny shift linkage needs adjusting or new bushings. It is common in many cars to lose the ability to crank in P, but works in N (or if you jiggle the shifter around N). My 1985 M-B was like that, plus made rattling sounds until I changed the plastic shifter bushings.
If really concerned, remove the NSS and test it with your hand. Should measure open from center pin to case w/ the tip pushed in and continuity w/ the tip extended.
