See the thread that John linked. JB Weld and styrene works well as a permanent repair. That’s what I used to fix the chassis break shown in my 1/31/21 post to that thread and it is still holding strong.
Does seem strange that the entire set has broken mounts. Handling must have been brutal. I do recall hearing that for a few years, right around the time your set was made, the plastic used by MTH was brittle.