We've got a Flymo "Pac a shred" (made by Husqvarna) which has been a great little tool. There's an adjustment screw to take up wear in the pressure plate (photos below). Recently, we needed to constantly wind the screw in to keep the plate cutting, and eventually the screw bottomed out. Something was seriously wrong!
The shredder has a toothed cutting wheel which squashes the branches against a hinged pressure plate to cut them. The adjustment screw is held in a hexagonal steel nut which appears to have been over-moulded by the diecast casing to hold it in place (put the nut in the mould, inject the metal, and the nut is trapped). However, there was hardly any material stopping the nut from pushing out - some small notches on the nut itself to engage the surrounding metal, and a thin flange on the outside. This flange had cracked off and the nut was pushed out of the casing. A very bad piece of design. Admittedly, I did wonder if this is some sort of safety feature to prevent overloading, but I'm not convinced.
As a quick job, I initially tried gluing the nut back in place with Loctite 638. If I have my numbers right, that should have withstood about 500kg of axial force. Although it worked for a while, it soon started pushing out again and eventually fell out. For a more permanent solution, I turned down the end of the nut and silver-soldered a small steel ring on it so there's no way for it to pull through. This seemed to do the trick, and so far hasn't caused any trouble.
It's amazing that the entire machine depends on this one weak point - if that fails, the whole thing is useless. It's not even as if you can replace that part easily either.