As far as I know the Stossschalter rattles a bit, that is normal. I have a spare one, that also rattles
There must be a reason that there are rust holes. Do you have a sunroof? If so, thru both A-pillars go the water drain hoses and end under the door, you can even pull it out behind the speakers in footwell. In case the drains are clogged, water rises there and rust starts , see here pictures https://forum.e34.de/thread.php?thre...uf+schiebedach
how to make new drain holes https://forum.e34.de/thread.php?thre...iebedachablauf
Under the doors all the wires go from rear to front/front to rear.
Trunk hatch wire loom in most cases breaks on the Touring, but also on sedans, you can also check that , some threads with faults caused by this
https://forum.e34.de/thread.php?thre...appenkabelbaum
https://forum.e34.de/thread.php?thre...appenkabelbaum
I would suggest you register on the German E34 forum and post there in which part of Germany you live and if there is someone near by with a diagnostic software which can diagnoze you car and then you know what is wrong and can repair based on that info.
For example in case you live in Memmingen oder München, contact Markus525itouring