Burned tetraethyl lead is lead oxide. I suppose some metallic lead might exist in there, but that whitish gray stuff on the valves and spark plugs sure ain't metallic lead, it's lead oxide or lead nitrate.
Being a transition metal has nothing to do with oxidation state, it has to do with the electron orbits filled to balance the the number of protons in the nucleus rather than the number of electrons any particular atom has at any given time.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!