I also have both of these knives. Bought them brand new and as you've noted the Maxamet Para 3 is so smooth. My Native, though, was very gritty and difficult to open. I drizzled KPL into the action and worked it back in forth for a few minutes. Whatever was in there worked its way out, because it is very easy now to open/close.
Same for me. I also did some small adjustments on the pivot screw and the action became better, but the sticky backlock still occured from time to time.
I decided to take it apart (WARNING: Spyderco guarantee extinguishs by doing so!). Found the blade sitting in its part of the backlock, and the spring linking this part with the backlock button. Couldn't really figure out where the lock gets stuck.
At first, I filed and sanded a little on the part with the blade (see picture below). With hindsight I wouldn't do it again, or maybe just with the sandpaper to smoothen the surface. The result of the filing was, that (in the open position) the lock sinks a little deeper on the knife side, and comes a little higher on the lock.
To my opinion, the part where the stick comes from most is here.
Rounded the edges of the spring and filed the surface of the lock where the spring runs on. Very careful and straight (important!) with a spyderco ceramic file. Just as much till the rougher parts became smoother.
Then I reassembled the knife with oil and used some red loctite for the pivot screws to adjust in the perfect position. Pressing down the backlock to unlock the knife is easier now. Maybe one of a hundred times it still sticks a little, especially when it stayed open for a while.
I hope, I haven't displeased Spyderco by posting these pictures. If so, feel free to delete them.
I also hope, I haven't used the wrong thread for posting this. If so, feel free to remove it.
At least, the Native 5 is the Spyderco I'm carrying today.