Fabio Driven: Something is definitely askew. I have a feeling someone either robbed the oring from this caliper, which would explain the missing o-ring. Or it was built on a late Friday afternoon before a holiday weekend. This caliper only has one "transfer port" to move fluid from one side to another. I was expecting to see two, but I'm sure due to it being a small 2 piston setup, I guess they only figured one was necessary?
Captain Handsome: there is a machined pocket for a o-ring to live in, but no o-ring! I was expecting to see a damaged/dry rotted oring I could bring to a parts store to get a replacement. I'll probably just bring the caliper down to see if they have a suitable one that fits. I never saw Guardians of the Galaxy.
tl;dr you are both right!