Where are the chemist?? I believe that there is no solvent that will "dissolve" pure lead, if fact aqua regia ( a mix of nitric and sulphuric acid) which will dissolve gold must be stored in pure lead containers. Soft solder on the other hand is an alloy of lead and zinc?? or other metals to meet some required property, so I would think the "solvent" in the cleaners attacks the alloy metal destroying the bond. JMHO --- John Can.