I have the same thing but I need just to wiggle the new key a bit the first time. The problem is that the lock cylinder and the original key are both worn together and the new key is sharp and catches on the worn lock cylinder. Lube and wiggling will probably do the trick and maybe wire wheel to round off the new key might be the answer but I don't know if I would risk that, maybe talk to dealer and/or locksmith.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)