I have the Juki MO DEV 654 serger, and it's at least 25 years old. Students used the same sergers in a college lab class I taught. They stood up to those challenges, rarely needed to be fixed and made a beautiful pearl edging and overcast stitch. The only downside is that you must follow the correct order of threading and threading isn't simple. After not using it for sometime, I watched a you-tube video and had no problem. It's a wonderful machine.
I also bought a new, top of the line machine. Gave it away and was happy to get rid of it. Good luck!