[Rilgamon]

Take a look at https://wow.gamepedia.com/API_AuraUtil.FindAuraByName

local name = AuraUtil.FindAuraByName("Shadowcore Oil", 'player')
if(name) then
print("Buff found.")
end

and

for i = 1, MAX_RAID_MEMBERS do
local unit = format("%s%i", 'raid', i)
end

local buffFound = 0
for i = 1, MAX_RAID_MEMBERS do
    local unit = format("%s%i", 'raid', i)
    local name = AuraUtil.FindAuraByName("Shadowcore Oil", unit)
    if(name) then
        buffFound = buffFound + 1
    end
end