FWIW, I had the same problem after installing my OE hitch 2-1/2 years ago. I inserted my dropout into the hitch, loosened all the mounting hardware (14 nuts and bolts?), put my floor jack under the dropout and carefully jacked up until it all lined up then tightened everything down.

Unfortunately late last year I took the car in to my dealer for some warranty work, and they pulled the rear bumper to replace a couple of the park sensors and when they put it back on it's now misaligned. When I questioned it I got the same response as many of you- it's not adjustable. When I showed them pics of the properly aligned bumper I'd taken after installing the hitch they said I just got lucky. So of course I had to refit my bumper again. A week later I took it back to the dealer and showed them the correct fitment and the service manager just shrugged his shoulders and said his techs don't get paid enough to do all that extra stuff that the shop manual doesn't cover. I'm now using a different dealer.

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'04 E53, 4.4 Sport
'97 E39 528i
'86 911 Carrera, track car
'96 BMW R1100R