Coolant leakage

I have a 1998 cadillac deville d'elegance. My car
has been running hot. Initially when i bought the
car it had a cracked head gasket. I invested in a
blue devil treatment which included the treatment
itself the radiator flush and a brand new oil change.
I also had bought a brand new thermostat but
mechanic failed to put it in. Now i have issues with
my vehicle running hot the check coolant level
sensor is coming on. I put water into the coolant
reservoir but its leaking water. There is no hole in
the original box but its leaking. I was told the
thermostat housing is damaged but i just wanted
to make sure thats my only problem. I investment
in a brand new water pump which includes the
gasket so will that fix my issue?