The printing itself is what keeps working. Owners with multiple Prusa machines say the Core One L and its siblings print well and consistently once they are running. The problems that come up are around getting there: one owner who went all in on the Core One, MMU3, Core One L and INDX said nothing went smoothly, from shipping onward, and that the whole rollout felt like a beta test even though the printers work great eventually. Another had the machine back at Prusa for service, including a belt swap, and missed having the upgrade fitted at the same time. Owners who hit these issues went to support, with mixed results: some got useful help, others came away more uncertain than before.
Long-term accounts are thin. The longest ownership reported here is about six months, most owners are still in the ordering, back-order or upgrade-planning stage, and several comments are about a machine that has not arrived yet. There is not enough here to say how it holds up over years, only that early output is good and the early ownership experience has been bumpy for some.