I finally got the swing arm back from the local mechanic.
I took the old driveshaft to him to install it in the swingarm and he noticed that there was a bit of slop in the U joints. So we had them replaced. These aren’t BMW parts but you can find people making them. I’ve since seen some on E-bay with grease fittings. My mechanic has been using these for quite some time now so I trusted his knowledge on this.