Effects of Adding Lead Additive

[don's 37]

I'm am writing in this concern for my father. My father owns a 1929 Model A. For 20 years now he has been adding a lead additive to his gas. Recently after the gas has switched to 10% ethanol he has been experiencing engine stall while driving. He removed the carb for inspection and found that everything inside the carb has a hard, black coating. It has the looks of tar but much harder. His tank screen and even inside the tank is coated with it. We have a feeling it's the lead additive. Now with using the new gas these days we think it's starting to loosen everything up and plugging up his fuel lines. Any ideas what my Dad can use to put in the tank to start eating this stuff away? Hopefully something can be done without removing the tank. Thanks! Don