That hose is otherwise known as the overflow hose. It like vstech said, you likely need a new cap, it shouldn't be leaking.

I'm pretty sure both of my cars have it dropped down the spring hole as well. The SEC had it out of the hole at some point, and it melted most of the way shut when it brushed the exhaust header. The hole makes a good place to avoid that happening!

__________________
-Josh
Testing the cheap Mercedes axiom, one bolt at a time...