http://www.wowhead.com/quest=11089/the-soul-cannon-of-rethhedron
this quest i was able to get all the items other than the flawless arcane essence, which is done by talking to Sar'this in terrorkar forrest. he will summons adds that you kill and the final mob drops the quest item. in talking to Sar'this, he does not interact with me and does not offer the continued help to get the final items required. see screen shot below
http://www.wowhead.com/quest=11089/the-soul-cannon-of-rethhedron this quest i was able to get all the items other than the flawless arcane essence, which is done by talking to Sar'this in terrorkar forrest. he will summons adds that you kill and the final mob drops the quest item. in talking to Sar'this, he does not interact with me and does not offer the continued help to get the final items required. see screen shot below