I have had some very good luck with Synthetic Oils. Here is a story. I had a '63 Impala, very hot engine, and a weekend driver. I had some leaks develope so pulled the engine and the pan. The splash plate was corroded. I did my thing with the seals and then started using Synthetic Oil. Castrol at the time, now Mobil. I pulled the engine again the next year, (nothing else to do
and guess what, there was no corrosion. The only problem, I see with synthetic is clean up. If you drip it on the concrete, it will not clean up easily.