I have never heard of a problem with leaking liquid. However, Arctic announced 3 or 4 months ago that a series of the Arctic Liquid II Cooler 280+360 had problems with the seal in the CPU cooling unit. The cause was a faulty vulcanisation of the seal.
(see.
https://www.youtube.com/watch)
Whether an AIO is affected can be determined via the Arctic website (see:
https://www.arctic.de/lf-service...). Only units produced between May 2021 and March 2022 are affected.
I have such an affected unit in my system and that is why I contacted Arctic. About 4 weeks later Arctic sent me exactly the service kit that is presented in the Youtube article by Gamers Nexus. On a Saturday afternoon, I bit the bullet and exchanged the seal. It took about 1 hour and was unproblematic.