IF you havent repaired a few SLR bodies, be aware that the timing is controlled by springs and escapements. Cleaning them and oiling them correctly without bending things, losing springs and air thin shims is risky. I have never been inside a nikkormat but I have opened 5 or 6 rangefinders and several medium format cameras and wouldnt hesitate to try...

If I was willing to throw the camera in the garbage, that is. I never open a camera to repair it without that thought in mind.

If the camera is precious to you, send it to a pro.