Unleaded gas predates WWII.

Lead was not put into gasoline for valve seats or lubrication.

It was put there for octane boost.

The valve seat bonus was a side effect discovered later.

Doesn't take much to fix the seat recession issue, Chrysler simply induction hardened the exhaust seat. But it was cheaper for Chrysler, and others, to not do this when they could let TEL solve the problem. Wasn't till the ban on TEL in gasoline that they started doing it. Save a nickle, kill millions.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.