Definitely the radiator.
How many miles is on the vehicle?
If the expansion tank is original, then I would highly suggest you replace it too. You don't want an old exp. tank to fail on you, it will be more costly than a failed clutch.
In fact, I would highly recommend you save up the funds to do a complete cooling system refresh.
Last edited by BimmersGarage; 01-10-2013 at 11:08 PM.