I got this as a first-time mod. Like the other reviewer, I wasn't sure what the o-ring was for (maybe the plunger tube, but that's solvent welded so IDK), but the spring and the lube work great. My biggest hangups were making sure that the plunger tube was oriented correctly (if you put it in upside-down, it will fire but it messes up one of the locks, so it only fires once). The prime is a little bit more difficult (to be expected), but I seem to have a noticeable performance increase over 70FPS. Overall, really nice spring upgrade kit!