This isn't an area I'm familiar with, but I do know they changed UnitAura in 8.0:
https://wow.gamepedia.com/API_UnitAura
It only has 3 parameters, and you can't look up auras by name just index. So UnitAura("player", 1, "HELPFUL") would give you the first helpful buff.
I think this exact issue has come up a few time recently so you might want to search the forum for more details on the new way to do this.