I heard the one about lead from Richard Golding. He said that when the concerns arose about lead content of glass for food and drink vessels, and that items had to be tested, Whitefriars lead decanters were unsuitable for wine or spirits, because lead leached into the liquid inside over time. So Whitefriars experimented with a lead free glass inner, and a lead crystal outer, judging the coefficients of expansion correctly so that the glasses matched. When first tested, they were fine - no lead. Six months later the same decanters failed the tests, because the lead had diffused into the lead free glass. I guess Whitefriars did not choose the inner glass carefully enough, because there are US patents for this very process, using an alumino-silicate inner glass layer.
It is not a case of lead trying to escape from the glass: so you will not find free lead under your lead glass items! It is diffusion of lead within the glass from a region of high content to one of lower or no lead content. The leaching is a chemical reaction involving the surface of the glass.
Regarding the effect of water, glass cutters know empircally that a drop of water can help start a crack. But more scientifically, research from the 1920s onwards has recognised the role of water in crack growth in glass. Here
is a link to an early paper (pdf document) that discusses the role water plays at certain stages of crack growth. There has been much work since - the effect is to do with modification of the stress field at the crack tip.