I peeled the actual lead off and then used the full flat edge of a Stanley knife blade held in a pair of mole grips to remove the actual glue residue, all that was left after that was a faint outline of the original lead position,if you persist this can all be removed using paint thinners or similar and plenty of elbow grease,I successfully removed lead lighting from a pair of patio doors using the above method.
Good luck.
Ronnie - Y.N.W.A., August 2011