Thanks north.. interesting! Per this article it seems ethyl chloride was used to produce TEL but the bromine compound was added to the gas/TEL mixture to reduce buildup of Pb compounds in the engine. I suspect only traces of chlorine made it into the TEL but seems Pb bromide was intentionally pumped out the exhaust.
https://www.britannica.com/science/tetraethyl-lead
Unleaded fuels probably got rid of the bromine but the alcohol had to increase the water vapor.. so probably more condensate but less corrosive without the halogens.
Back to topic, I don't think I've replaced any exhaust part on any of my cars because of corrosion in the last 20 years. I do remember rusty mufflers and tailpipes being common before unleaded gas. I suspect an aluminized steel exhaust system would last a long time.