end tanks are just that. the sides of the rad, they are plastic, one side houses the trans cooler, the other side in some cars can be a oil cooler.
they can crack and leak to the lower cross member area under the rad. sometimes they wont leak till the cars all warmed up too.
you should just go do a free rental deal and pick up a pressure tester, it pumps air into the rad, and has a gauge on it, so you can see if it looses pressure, if its loosing pressure, its also forcing it to leak out somewhere.
