One way to dissolve lead solder given to me old timer is to take 4oz20% hydrochloric acid and add 1/2 oz ferris chloride, worked greatfor me many times.
Good luckBill Wismarwww.wismargallery.com
I have always removed lead with muriatic (hydrochloric) acid. Tryto use it outside. The fumes tend to rust things inside.