I compared it to mine Cameron, and it looks like your bogie is kaput. Is this item still in the Marklin parts database? A new old stock bogie may be available. Even if you found the broken piece from the center hole contact, cementing it back in so it doesn't bind the metal post Will be tricky. If the wheels stay on when rolling and running, then the broken frame end in the picture is not detrimental.a black wire solders to the copper piece., and a red wire to the center pin inside the hole.
The other option is to eliminate this mechanical reversing switch and install a function decoder which could also control interior lighting. Newer Marklin control cab cars use it.
I looked it up and it was reissued this year. The parts list doesn't show the bogie in stock, only the contact pin, and insulator.

I havn't done one, but I have installed led kits in my cab car. Because these have led headlight/tail they have hte needed resisstors already. If you use Marklin kits, they have resistance as well, so no blinking. You only need an mfx function only decoder. If you don't habve an MS2 or CS3, an older type can work.