I have never heard of them eating lead before, you'd think the lead itself would kill them!
The only thing you can do is remove the food or water source to make it unappealing for them to go after your house - spending the money to make those vents inedible will help.
However, another poster had it right, if you can figure out the one or two that are leading the charge and remove them, the others often show no further interest.
I had squirrels tear into my soffits and get into my attic, after doing the repairs I caught one tearing into it again and shot him with a pellet gun, over the next few days I shot a few more who were also in the same area, since then I haven't had a problem.....with the squirrels. A nosy neighbor DID call the police on me and I had to have a conversation with them.......the upshot of that was I took my new pellet gun back to the sporting goods store and got my money back.
My gun was a Gamo, with a killer scope on it, shot over 1100 fps, and worked a treat on the little buggers - it was accurate and deadly. However, many times when you shoot a squirrel it doesn't just drop dead, it runs around all "squirelly" .....this is what did me in, I hit one and he dropped to the ground and went nuts right in front of a neighbor woman who happened by while walking her dog. ooops.......