I have an R171 and the spare key is useless. Investigation revealed that ALL key tracks had previously been blocked other than for my main key. MB dealership have been unable to unblock the tracks to allow access to my second spare key. The have tried a process of 7 hours using a special key supplied by MB with security codes but this only managed to work the remote function, NOT the ignition. They now say they need to replace the ignition at a cost to me as they say this is not warranty despite there being an obvious fault with the ignition (not unblocking). The model is 2006 and still under warranty. Can anyone offer any help or advice??