heater core is just that, just that part needs to be changed. if you can build a model you can open this up and change it. your working with plastic parts the whole time till you get to the core. remove all the small bolts, pop a part off. its just uncomfortable to work at due to your on your back hanging out the door with a light next to your head so you can see, then get up and find the bolts on the other side, so its a back and fourth game for a few hours.
it "WILL" go back together faster and easier then it came apart, i guarantee it lol