That is my plan. The dealership has it but they know I am not going to pay for another item, which is why they replaced the radiator cap and had the radiator cleaned without any charge. At this point I know they don't want to ever see the car again.

In answer to your question- there is no traces of oil and the head/block joint. The area was actually checked over last year by an independent who I instructed to check it over as Mercedes told me I had a head gasket leak... turned out there was no leak (or none that he could find). Supposing I had this issue, would the car only overheat when I am in idle and then return to normal temps when driving faster?