Barry hit the nail on the head. Lead can have an acid residue that can cause problems. A class I took from Gene Winfield quite a few years back, he had an interesting story about Cadzilla and the failure to clean the lead properly that a builder had used when building the car. The paint start peeling. Winfield had the pleasure of fixing the car. Coddington was the rookie with lead. His story, not mine, just passing it on.
"When I was younger, I could remember anything, whether it had happened or not." - Mark Twain