The QMC tram had similar defects to the Yan detachable chairs, one of which failed at Whistler in 1995. Mammoth modified the Yan detachable chairs (2 at Mammoth and 2 at June) but removed the QMC, which was presumably too expensive or not practical to repair.
The 50+ year old J1 is indeed a sore point. Even though June is a quiet area, lines can still stack up to download it at the end of the day. It's also not a comfortable ride for many beginners and children, who are and should be key target customers for June. Mammoth plans to install a modern lift, but that was delayed by the drought years. I'm guessing we will be seeing some capital investment at Mammoth soon, but where replacing the J1 falls on the priority list I couldn't say.