That seems like a good price. I doubt you can tell by looking at the shutter firing so the seller probably didn't know. Probably dried up lubricant.
Anyway, I would not tinker with it myself and send it out for a CLA, making sure the person doing the work is competent in working on the Nikon.
When buying used, especially as old as this is, you should always allow for a CLA or not buy it.