I have owned almost every Salt Spyderco out there, and tried almost every model (including the discontinued Catcherman, and Spyderhawk) on many occasions.
All of them flip and work well, not as smoothly as other Spydies I have but definitely none of them had problems. I never put oil on any of them, just water and soap.
But, all of the Pacific Salts I have (a black and a yellow SE, and a coated SE 2015 model) were stiffer when I got them than they are now. The Spyderhawk was the easisest to flick open, and even then it also has improved with time.
After some (quite a lot, in fact) of use all three of them have smoothed out, and after frequent cleaning, dirty days etc. they improved a lot as far as action is concerned.
So, as others said, I say give them time! It just gets better and better. Can't go wrong with any Salt, really!