If it's the rear main leaking the only additive that will fix it is a new rear main seal. 30 min job might be a lot ambitious but the seal itself is cheap as chips.
sorry read that with lack of sleep, was thinking extension housing seal
rear main seal, hand over weeks pay to a mechanic and up to two days off the road
I had similar looking oil markings in my WH LS1 and thought the worst, ended up being the PCV hose had perished that runs behind the top of the engine. It's the hose that goes from the rocket cover to the front manifold.