Just wrote lengthy reply. Then deleted it by mistake.
If you are confident with this sort of thing, it is quite easy fix.
If you are still under warranty send it in.
The ballbearing sits on the contacts. The spring pushes the ball down. It matters which way round the switch is aligned. I used a tiny bit of superglue to keep the spring inside the plunger (tiny amount) - try it without the glue for a bit, it will annoy you, then you will know what to do and why. When you realise what you need to do and you are comfortable with it, a tiny bit of superglue will seal the grey casing back up again.