On the subject of leaded gas, check this timeline out. It will amaze you and even might make you mad.
http://www.thenation.com/doc/20000320/timeline Back to valve seats, a little something from the EPA
http://yosemite.epa.gov/r10/AIRPAGE.NSF/0/adebd4b8879d36bc88256c0800760bf5?OpenDocument
