Well, the good part is, the guide rail cannot have fallen down as the engine idles nicely, although i only dared let it run for 20 secs Sunday, as i was pretty sure this could be(come) serious.
After looking closer at the exploded M110 drawing in my Haynes,
i can see that it clearly shows the guide rail (by name too).
But i'm not sure i can drive the pin in again, as it can be pushed just as far in by hand, as the pin just below it.
Maybe a good shot of Loctite wil help keeping it in place (hope the innermost end is not broken off) ?
Otherwise I will try to find a MB dealer who can fix it or maybe borrow/rent me the correct tool.
Thank You very much.