On these diesels 2 of the six contacts on ignition switch are not used. So you can change those two new contacts on the most worn positions. You can just knock out the contacts from the plastic casing and push back in desired position. Usually the most worn are high current Terminal 50 (starter activation) and Terminal 15 (pos. 2) contacts. A few years ago I had the same kind of switch failure when starter occasionally said nothing.

https://photos.app.goo.gl/7najyUasWbpYgjcx7

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey