Check out this link.
O2 sensor electronics testing
There is also another link where someone with a V-12 rebuild his.
http://v12uberalles.com/throttle_actuator_rewire.htm
I bought the ETA cable harness, but before I got around to replacing it, my car was totaled. I ended up giving the harness to the tech at the dealer who was dealing with a 500E with a bad ETA harness and an owner who was at the end of his rope throwing money at it. The ETA cable is not a part the dealer normally stocks. The tech had an even bigger problem because the ETA canon plug connector on the 500E was not the 90 degree type like mine. I'm not sure if he was successful in working around this. He said it was a good customer and was going to do what he could to keep him happy.
There is a paper-thin gasket for the ETA and a rubber boot as well. They should be changed but they are really cheap at the dealer.
Good luck and let us know how it went.