What is the best lead additive on the market for four-star petrol?

I have a 1958 Bentley S1. What is the best lead additive on the market for four-star petrol?

Should I use a petrol additive in my classic Mercedes-Benz?

I have a 1966 Mercedes 230SL, which I use lead substitute whenever I fill it. Should I add a fuel system cleaner every so often and will the lead and fuel cleaner additives cause issues between them, or...