coolant hoses

I have a 2001 mercury sable 3.0 dohc or
something like that... My car started to
overheat on my way to work. Pulled over
and. Had to get it towed back home. My
mechanic said that it wasnt the thermostat
that needed to be replaced nor the upper
hose. However he still changed the
upperhose. But there is a piece that sots
directly on top of the upper hose that
connects to it. I am trying to figure out what
the name of that hose is because nobody
knows the name. That is where the leak is
coming from. Advanced auto and a few
other places say i would have to get some
kit that costs about $120 just to fix this one
and a half inch tube. But yet they dont have
this tube separate by themselves or they
dont know the name of it. Looking for
answers and ive been down for a week now.