No expert here either. Recently, I tried a Dripbox2 as part of a promotional deal. This issue the OP is having was not even an issue for me. I simply do not like the shape and few other minor things which put me off of it.
Looking at the photos, reading the situation & context, I would say you ought to be safe. The rubber grommet appears to be an extra o-ring of sorts. They may have tipped a container of o-rings over the packing process. It seems like one of those one off incidents that can be put to human error in an automated factory, oops, poop happens.
Now, please excuse for saying this but if you are not comforted by my explanation and still feel unsafe, disregard my explanation. I possibly might be wrong altogether and can admit that. For me deduction of troubleshooting goes to Ocham's Razor, what is simplest ought to be considered first. I would set the grommet aside for later use in an atomizer or another mod that might need one, vape on the Dripbox2 if you find nothing else 'hinky' going on.
I agree with
@CircusClowd, it only takes a second for the nasty breath of an accident to sweep over us. At the same time if you don't try, you never know if you can make it over the wall.