You want to anchor the tooltip and you can just use the standard GameTooltip.
Code:
f:SetScript("OnEnter", function(self)
if (UnitBuff("player", 1)) then
GameTooltip:SetOwner(self, "ANCHOR_LEFT")
GameTooltip:SetUnitBuff("player", 1, "HELPFUL")
end
end)
Just noticed you did anchor the tt but it's best to do it just before you show it because it might have been moved (re-anchored) by another process.