74 Duster won't start

I just had the same issue with my 72 dart. When it got cold out it seemed like I had to find a sweet spot in the shifter selector until this morning which there was no more sweet spot. I read in another post to bypass the neutral safety switch by jumping one of the pins on the starter relay to ground which got the car started. But what I would like to know is what stuff I should start buying (neutral safety switch?) or could it be an adjustment or is something need to get lubed ,its funny that it started when it got cold (below freezing)