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A new shutter is at least as likely to fail as one with 170k operations on it. Don't change until you have to. I had a pro Canon shutter die in under 2k operations (yep, just two thousand), and the replacement was defective when I got it, and it's replacement was better but still wasn't as good as my other cameras.
Statistically, a lot of things are most likely to die when they are very young or very old, with a lesser failure probability in between.
If your D3s is new to you then do some tests at maximum shutter speed. Shoot some plain blue sky, perhaps a little underexposed, and evaluate by looking for uneven tonal bands. They'll show up most easily as you rotate the image 90 degrees ate a time. If a shutter will die gradually then it will most likely start at the faster speeds and then deteriorate at progressively slower speeds too, picking up speed as it goes. Otherwise, it'll just fail suddenly and catastrophically, but at least that'll be easy to spot.