While it is possible to do the quest chain up to this point by speaking to Medicus early on, this last quest in the quest chain will not be available until all previous quests has been done for Lord Sheckt and Quartermaster Ulrothk . The quest Is There a Shaman in the House? needs to be completed to unlock this quest.
Before you grab the Spirit bear make sure no one else near tries to grab him too. If you grab the bear and someone else starts the quest or tries to grab the bear you will lose yours, even if they are not grouped with you. If you fail, hail Shaman Medicus again to repop the projection.
Using the Sokokar post can work to complete this part. The bear will not be there when you land, but if you go to the ramparts, the quest will still update. Also will be fine if you delete the quest and then pick the quest back up and return to ramparts, it'll update.
It seems that as long as you leash the bear, it doesn't matter how you get to the ramparts. I took the sokokar but got off to get a shiny, then rode to the ramparts on a flying mount. Even though the bear was not physically there, it still updated the quest when hovering around the entrance to the ramparts.