Overheats and hose failure on 2001 Volvo S40

I own a 2001 volvo S40 I have experienced some overheats it was found that oil is getting into the coolent. The radiator was replaced and also the head gasket, but still have oil coming into the coolent. What are other likley causes as the mechanics are are not sure where the oil is entering. The cars has run pretty good during all this as well. Any ideas