I voted for block slow drip.
That was on my first block, that was a heatsink on which I bonded a fiberglass cage. The adhesive used was quick epoxy, and it didn't hold the long term water exposure, becoming very soft. One of the barbs loosened and a slow drip developed over the back of the gpu. It was so slow that every drop always evaporated completely after the next. That caused intermitent annoying graphics behaivor only when wet.
This was more a manufacturer mistake than an user error, even if in this case both were the same
My lesson was not to trust on a product marketed properties; every material deserves a proper test on the specific aplication before being accepted.