you need a special tool - the ball is probably just spinning inside it's joint, there is a very slim flat section that you can get a spanner around but you need to figure out what size spanner it is and grind it down so that it is about 2mm thick (I forget what size spanner it is), Or you can push the rubber boot out of the way and stick a pair of robogrips on it, I recommend only using the robogrips on the teardown rather than the install though......

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2004 E53 4.4L N62