Is the tool you are renting from AutoZoo made for MB ball joints? Performance products rents out the proper MB tool, but I have heard that sometimes they send out a worn out tool. If it is just the regular ball joint tool, it may not work. I borrowed a regular ball joint tool from a buddy who is a mechanic at a Ford dealership. I had to make an adapter to be able to use it at all. The shape of the MB steering knuckle is such that you can't really get the regular tool in to grab the ball joint. I was replacing bad lower ball joint on '83 300D and the job was such a pain and made me so mad I have not gone back to replace the other side after I got the first one installed. I did go ahead and remove the spring and replace the bushings and all rubber pieces on that side while I was in there. Really need to do the other side now as daughter is complaining (with good reason) about the sloppy steering. BTW, I have found the ball joint on the upper control arm to need replacing as much as the lower joint. They are not too expensive and are fairly esasy to replace. Plus they are easy to spot. Just jack up the car and grab the top of wheel and try to move it in and out. Then try to move it up and down. try again with a jack under the lower control arm. It will scare you when you see a bad one.