Hi Nicole,
It looks like the
center-column (the extending part)
alignment stud (to keep it from rotating while extending) came off after the
retaining ring (that washer-looking thing that broke in half) failed. They should both be metal parts, held in place by a screw going through the alignment stud and into the cast-metal
spider hub (the big metal part that all three legs attach to). As you noticed, without this alignment stud there, the center column will rotate as you try to lock it, and never lock down.
However, just so you know, tripods are not assembled with superglue! You may keep it from falling apart for now, but the next time you use the tripod in a normal fashion, it
will break again. Superglue gets really brittle after a few days, and those parts are intended to take a lot of pressure (but more than you can apply, which is odd, since you broke them).
Rather than continue using it,
contact Benro directly (sales@benro.com) and explain what happened with photos, but be sure to explicitly ask for "a replacement spider hub and center column." Your legs are still good (!), and can be unscrewed from the broken hub and put on another one of similar size in about five minutes using two tools that come with all the tripods. The manual for the tripod even has instructions on how to do this!
If you don't hear back from Benro in China (usually takes a day or two, outside of Chinese holidays), then
PM me and I'll give you the contact info for the
owner of the Canadian Benro distributor. I know him and deal with his staff for lots of different products as a reviewer, but I also know his office won't have spare parts on hand, so he would end up contacting Benro for you, that's all. So if you don't get a response, he certainly will!