I have the same thing - vibration under braking - replaced the front wishbones with the Meyle HD's. Got worse, I guess because now that they are solid it is making the culprit more pronounced. I'm pretty sure its the ball joint on the upper control arm which I will be replacing soon.

If you can get both front wheels off the ground and get a friend to give one wheel a good left to right shimmy as you have a look at all the suspension parts you'll quickly see which one is bad

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2004 E53 4.4L N62