After being frustrated by the unreliability of my Zippos to light, I did what must seem obvious: I cleaned them thoroughly. First, I emptied the cotton from the interior, removing the retaining spring and flint (it's not needed to take out the wick), I placed the firing mechanism in a small jar filled with alcohol (any alcohol will do), shook the sealed container a bit after it had time to sit, them removed the mechanism and scrubbed it down with an old toothbrush, giving special attention to the igniting wheel, where gunk is most likely to collect. Rinse, dry, reassemble, and voila, the lighter ignites like brink new. Obvious, but I'm getting old, and the obvious sometimes escapes me.