So I took my CX3 to a dealer service center for its 1st oil change last week (2200 miles/6 months) using synthetic oil. I was surprised that the dealer recommended using an engine oil additive (BG MOA). I've read that these additives are useless since the synthetic oil already has the same additives. Is this correct? It's only $25 but I'm wondering if should I even trust this dealer - maybe they frequently try to sell unnecessary products and repairs. Or maybe selling engine oil additives is just a standard practice. Let me know what you think.