I think the unleaded petrol also shortens the life span of the entire car engine, at least for cars meant to be driven on leaded petrol from the beginning. 
It does they make replacement additives that don't contain lead to better lube the pistons
I thought they put catalytic converters on the cars as well so that they can take unleaded petrol instead of leaded.
They need to use unleaded gas in cars with catalytic converters because lead fouls the catalyst in the catalytic converter.
The older cars (models before 1975 in the US) without catalytic converters used gasoline with tetraethyl lead to inexpensively increase the octane rating of the gasoline as well as to help lubricate the pistons. I think I remember my dad telling me that a TEL gasoline additive was available for a short time after the switch. TEL is extremely poisonous, however.