When I bought this car it had no rear wiper on it and just this piece which I assume is from the past one and is just rusted there anyone have any ideas or pictures of what this is normally supposed to look like?
Same happened to me in the spring.
Motor was still working so here's what I did.
That's the nut from the old wiper arm stuck to the motor shaft.
I used a Dremel with a cut off wheel, very carefully cut partially through on each side, then used pliers to twist the half bolt off from each side.
Cleaned up the threads with a small Wire brush, anti seize grease before installing the new wiper and away you go.
This...
Exactly what I had to do. Dremel the nut off, clean it up with a wire wheel and the new arm should slide right on.
You might need to use some force to get the wiper arm on far enough.