MK2S upgrade LM8UUs bearings question
I've just started performing the MK2 to MK2S upgrade, and I've noticed that the supplied LM8UUs bearings look exactly the same as my old LM8UU bearings. I don't have the means to assess and compare the old and new rods, but the new bearings also have the "LM8UU" imprinted on the sides (same as the old ones), rather then LM8UUs as one would expect. Is that OK?
My printer was purchased in October 2016.
Re: MK2S upgrade LM8UUs bearings question
I am not sure what else besides LM8UU you expected to see on these bearings, as this is what these bearings are called. But here's a recommendation: gather up all the bearings you got, put them on one of the new rods and try them one by one how they slide across the rod. Pick the ones that give you the smoothest movement. Between 2 full sets of bearings, you should get enough decent ones. Or take the opportunity to replace them with some more reliable brand altogether. Misumi is always a safe choice.
While you still got them assembled, you might also check into the proper procedure to clean and pack them with grease before assembly. There should be instructions on Youtube if i am not mistaken.
Re: MK2S upgrade LM8UUs bearings question
LM8UU <-> LM8UUs
if you're searching the internet, you won't find a definite difference between these two. so the "s" might indicate either special, silent, selected or stainless steel. choose what you like 
but until now I didn't came across an LM8UU that was not stainless.
so if you need replacements: go with stephan.k's advice: get two cheap sets of standard LM8UU and choose the best for the dedicated rods.
btw.: even in a mitsumi bunch you might find some that are not pristine.
dem inscheniör is' nix zu schwör...