1st: I'd have the trailer inspected for frame damage. To bend a king pin takes a lot of force. I've only seen 1 bent king pin in 19 years on a semi trailer and it was from abuse. Had a recall once for improperly heat treated king pins that had to be inspected for cracks. Point is, it's the same standard pin and a 5er is such a light load. I would suspect (guess) that to bend a pin, you broke something and hence an inspection is warranted. Maybe they did not get it "true" before they welded everything up, but you still need to get it checked out.
2nd I'd check with my local dealer and see if they had a new pin box (which fits my trailer) that they removed from someone's 5er when they upgraded pin boxes. Probably get a pretty good deal on it and then you won't have to worry about the bent one.