upon reading the responses, I went back for a closer look on the top edges and there are no
obvious tool pry marks that would exert that much force. Also, the photos show
that the expanding force came from within the cavity, pushing outwards. I found a crack
in the bottom of the cavity on the right (red arrow) that I did not notice before – and it is definitely pushed out by force.
With that evidence, I am pretty sure it is from freezing. And that Mississippi Mud probably didn’t help much either.
with a little finese and poxy putty, it will be as good as new in a couple of days.
Thanks to one and all for the feedback.
.