Originally Posted by Zuber
There is no 'wear and tear' that fails like that. Look very closely at the reservoir and see if it's cracked. If the shop over filled it, so there wasn't enough air space, it could blow up like that. But, that's a major mistake to make.
The impact of a 500+ lb. bike on a sharp bump and a over-filled hydro-locked shock is the only way I can imagine blowing the reservoir off like that.