Yeah, I'd highly recommend a good clean to the valve body and those two pipes going from the transmission to radiator. It's definently worth doing. It's funny how dirt can affect a valve body so much that you would have no clue where to look. What model/year is your BMW? Let us know how it goes with your car!
Yeah, I've done a heap of work already on mine. Head gasket, water pump, radiator, transmission rebuild and goes on. But I still love the car, a great pleasure to drive when it goes properly