Elixir of Iron and Ruin buff trades.
Not all of them obviously but switching over the Tenacity and allied MS buff from Iron for the health of Ruin seems where the two items should be at. Each person who's getting the elixir needs what the other is selling.
While tenacity is good for tanks being able to take more abuse seems better. A split pusher needs to get in and get out so the MS for minions would help them greatly and the extra tenacity will allow them to not be held down by an enemy defender or a collapse.
This has just been something that has bothered me for awhile now with the two elixirs. Its an obvious flaw that should be changed. It would be as bad as the elixir of sorcery giving life steal while the elixir of wrath gives mana regeneration. Not to mention that Elixir of Iron gives a false sense of security with very little benefit for the entire team.