......Personally, I never reuse an elastic stop nut. New one any time one is removed......
Years ago, as a young maintenance engineer at a paper mill, the ink only a few years old on my Mech Eng degree...
and not long after I'd sat through an eye opening intense seminar (1 or 2 days) on threaded fasteners, where I had learned that these sort of nuts should NEVER be re-used...(because the plastic locking insert can't do it's job the second time around)
....Anyway, I was walking through the maintenance shop attached to the light school where I was active and spotted the young junior A&P re-installing a prop on some customer's airplane and he was re-using those nuts.
and me being conditioned with the nearly constant safety training at work which taught to say something if you see something.... well I said something. And was summarily dismissed...he was "certified" and I was not, and all of that.... clearly he'd not gotten the same safety training. I probably wouldn't have cared much had those nuts been safety wired, but in that application they were not.
Anyway it was in that same threaded fastener class that in a small way I had a life changing epiphany.... that nobody knows everything there is to know about any topic... I had grown up wrenching on cars and boats, rebuilt several engines...then a pretty good GPA on my AAS and ME degrees with elective classes in machine design which included a fair bit of study on threaded fasteners....
Well I thought I pretty much knew everything there was to know about tightening lug nuts on a car (or whatever)... I had my eyes opened in that class!
and I'll add this which carries into your "never re-use those nuts" rule ....... I learned that a torqued nut deforms. The loading on the threads in the nut tapers off over just a few threads...with something like 80-90% of the load being carried carried by the first 3 or so threads.....most by the first thread, a little less by the second, and so on... (I forget the exact numbers off the top of my head now)
So nuts are softer than the mating screws by design, and these first few threads deform. If the nut is re-used, the torque required to get the same preload changes, and the loading profile within the nut changes, etc...
All of this probably doesn't much matter in many non-critical applications, lightly loaded where torque and preloads don't much matter, etc...
but still, I find it to be something that a lot of folks don't know...
but looks like what I will do 
