Question AIO Cooler empty of coolant? How?

Long story short.

My mother's PC was over heating, and I found that the closed loop All in One liquid CPU cooler (Corsair H60 120mm AIO Cooler) was empty of coolant.

It has been resolved, but how and where did the coolant go? I'm no chemist (obviously).
 
check the motherboard case for resedue
did you disassemble the cooler from the motherboard? eventually the cpu was/is wet

usually it dips just a few drops over time a year or so and vanishes

check the aio for bad fittings like
View: https://youtu.be/iG_w9jrBMVM?feature=shared
Replaced AIO, cheap enough. I was going to refill it, but my Amazon order was on the way already.

No evidence of "drips or leaks" in the case. The case was quite dirty, so I would have seen rings or spots where coolant would have gone.

There was a small blob of something on the lower SSD, whish easily cleaned up.

Anyway, all good now.