Nice write-up, Uwe. In my June 2023 Sky & Telescope article titled "Far-Out Globular Clusters", I treaded lightly on the origin of M53 & NGC 5053 by writing "While there is a high probability that M53 was formed long ago in another galaxy, figuring out more than that has proven very difficult. Nonetheless, it does seem to have a traveling companion less than 1* away and closer than 5,000 light-years away from it in space. William Herschel swept up NGC 5053 for the first time on March 14, 1784, immediately after observing M53 with his 20-foot (18.7-inch mirror) reflector."

Hopefully in the next decade scientist might be able to pin down it's exact stream origin.

Scott H.