1990 240dl b230f 180k mi

Did plugs wires cap and rotor today....

Putting the new cap on and it didnt feel super tight, but its been a while since Ive worked on one of these.

Fit it in & it felt right, clipped it in place and started the engine.

Ran great, no issues or anything.
but noticed the cap bobbing around ...

Video here...
https://youtube.com/shorts/X0j-zTMIJ3o?feature=share

Again. Ran fine, revved it a bit... No problems and sounds fine...

Is it supposed to fit like this?

 

No, it's not supposed to move. The rotor button could be hitting inside for some reason - maybe the cap is 180 degrees out (the notch is not aligned)
or did you use 2 different brands of parts? (cap and rotor)