crack onto vs lead on

crack onto

verb
  • To flirt with; to approach and speak to (someone), seeking romance, love, sex, etc. 

lead on

verb
  • to encourage with the illusion of a romantic relationship. 

  • to mislead, to try to make someone believe a lie. 

  • Used other than figuratively or idiomatically: see lead, on. 

How often have the words crack onto and lead on occurred in a corpus of books? (source: Google Ngram Viewer )