Originally Posted by Jpm757
The only "Lycoming" approved additive is LW-16702 Anti scuffing agent. It adds about $35 to the cost of an oil change. However there are several "FAA" approved additives such as Avblend,
The Aeroshell Plus grades (i.e. W100+) contain LW-16702 so you don't have to buy a bottle of additive separately.