Just discovered a loose front ball joint on the lower left control arm. Anyone change one of these before?? The Parts Bin has aluminum and steel ones. Steel half the price of aluminum. Whats the advantages of going aluminum besides unsprung weight savings if its possible anyway? Bentley says you need to replace the whole control arm and recomends replacement in pairs! What the heck does that mean? Both sides or upper and lower control arms. Sometimes I wonder about Bentley!