Took my 08 GXP to be serviced at one of those quick change places yesterday. They told me my differental grease needed changing and showed me the diff plug. Oil was black so I told them to change it. I also told them it was a limited slip rearend. They said they would look it up and get the right oil in. When they got done I asked them again if they got the right oil in rearend because it was limited slip. They said yes and I drove off. I did some shopping and after I has driven 3 miles, I did a sharp left and I heard grinding in the rearend. I took it back and they admitted that they didnot put in the friction modifyer. They added the friction modifyer but the rear end still makes a grinding noise when turning sharply left or right. What happended? It was only driven 3 miles without the friction modifyer stuff......