Hello, Wendell,
No & No (No)
No need for lead additive in your gas.
No need for Marvel Magic Mystery Oil in your gas.
No need for any Snake Oil in any 235 that is in good condition, and is well-maintained, and is well-tuned.
What is your "
top end"?
If you take your valve cover off and run the engine, does oil drip/leak out from the rocker arms?
Use an oil filter.
Use detergent oil (you might want to drop/clean your oil pan).
Use a gas filter.
Change the oil and oil filter every 3000 miles (or, earlier).
Keep you engine tuned (valve lash, carburetor, ignition system, timing).
Make sure your road draft tube is clean/clear.
