That is the "upper" radiator hose.
I assume you have already tried tightening the clamp.
You could drain some of the coolant into a clean container by twisting the petcock at the bottom below that hose.
Then disconnect that hose and using tin snips or such, trim about 3/4" off the end and reconnect it.
Put the coolant back in.
Might fix it, might not.
If not, then look for a 2003 MB slk32 upper radiator hose.