Tetraethyl lead was put into gasoline to increase the octane.
PERIOD>

It was back in time after another energy crisis, like in the 1920s.

You could go back and read about it if you wanted to.

The lubrication of exhaust valve seats was a happy coincidence.

All aluminum heads have hardened valve seat inserts for both exhaust and intake valves.

Really, I don't know where some of you guys get your wrong ideas.