Thanks Craig. I see what their talking about. The stock injectors have a groove that the o-ring sits in. The Bosch II injector does not have a groove and the o-ring could possibly come off and be left in the injector housing. I doubt that it would fall in though. If it came off, I would think you could get it out with some kind of pick. I'll leave the cap on anyway.
They were shipped with black covers over both ends.