In all the instances of bolts being used to jerry-rig a repair, this is only a get you going solution.
The original plastic bolt has a hole through it for pressure relief and you should replace the housing at the earliest opportunity. Unfortunately, even though it's only the plastic screw that needs replacing, you cannot buy it separately - you must buy the whole housing.
This is actually not a bad thing - over the years of heat cycles (hot diesel, freezing winter), the plastic will have become brittle, which probably explains why so many bolts are now snapping. On the other hand, ham-fisted mechanics who can't read will account for more breakages (the flange on the screw is clearly marked up with the torque of 2 Nm).
Cheers,
Mike
PS There was a move some time back to get these screws made up and I think our resident metal turning expert and social co-secretary A2sumo looked into having them produced in aluminium too. Don't know what became of the idea though.