I've been running LFR DS every week on my pally trying to get Gurth for some time now and from 10+ runs all I've had drop is the same pair of shoulders (twice) from Spine. I've not seen 1 piece of loot from Ultra, Blackhorn or Madness. I'm starting to wonder whether there's a bug somewhere because surely this isn't just down to luck.
Remember doing LFR DS back in Cata, 50% of the time Gurth would drop, many times it would drop twice on the same run, yet now it's like trying to farm for a mount -_-