I may have miss this information in all the great posts but I think it bears repeating.

Do not use Full Synthetic Oil with 100 LL fuel. In case some don't remember the Mobil 1 oil fiasco and that it was removed from the market after several aircraft engines were damaged.

As I remember, Synthetic Oil will not accommodate Lead residuals and will plug up the oil holes. That is why Shell has offered only a Semi Synthetic.

Full Synthetic Oil works great with NO Lead fuel.

Jim Hergert
N6XE, "An Sex Y" L4P
A 15w 50 Semi Synthetic user with Full TBO hrs on at IO-520 and 140 hrs on TSIO-550. For what that is worth.