There is a fair bit of engineering in the original thrust bushing design and they are part of a pretty well engineered suspension. It would be nice to know exactly what a person is giving up when going to a solid bushing. I would say there is definitely some tuning of the flex going on under braking and acceleration in the original.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)