Did a Seafoam treatment the other day and put some into the brake booster vacuum hose. While doing so, I noticed some of the exhaust smoke coming up from behind the engine where the rear spark plugs were (It's the V6 2.8L). Would this just be a bad exhaust manifold gasket, or something worse? It only did it for a short time and I didn't notice anything else unusual.
My Fiero: 1986 Pontiac Fiero GT, V6, 4-speed manual