Timothy wrote:
Is the implication that it could happen any time, if water gets in the hydraulic system?
Yes, but I would really be interested in just how the water got there in the first place !
Checking & cleaning it are probably an Annual or 100 Hour inspection items that got “over-looked” .
Michael wrote:
It’ is VERY likely that water got into the system and accumulated in the bowl. It then froze and split the bowl open.
Is the implication that it could happen any time, if water gets in the hydraulic system?
Yes of course freezing water would make perfect sense.
The wire is surprising. It is also “flapping around” and the joints are protected by no more than the original sheath with some obvious points of mechanical failure.
That’s a small strainer and the safety wire secures the bowl that is obviously screwed into the base.
It’ is VERY likely that water got into the system and accumulated in the bowl. It then froze and split the bowl open.
That corroded aluminium fitting (I have no idea what it does) does look like it has pressure in it, so it would leak fast.
Should the hydraulic cylinder be resting on the pipework beneath?
Yes that so sooo wrong wrong wrong; whoever did it should be shot. But the unsecured wire at the top isn’t much better… and the wirelocking wire doesn’t look like it goes anywhere 
Should the hydraulic cylinder be resting on the pipework beneath?
This is the object that cracked, and apparently the crack was approximately as indicated by the red line. It was said by the engineer to have been sudden, and sufficient to dump all the fluid in one go.
Ahhh, yes the elusive mouse milk – have fun with that ! 
If you can, please take a picture of the break spot.
No. I can’t say any more than that. I do a pretty thorough check and there was nothing to be seen.
I am meeting the Chief Engineer tomorrow (he is going to teach me how to milk a mouse or something ) and so we’ll have the cowlings off. I’ll ask him to point out exactly where the break was.
Timothy wrote:
My guess is that the pump operated at the beginning and end of a few flights and pressurised it out.
Hmmm, and the pre-flights did not catch the streaming hydraulic fluid ?
