plugola vs slush fund

plugola

noun
  • Undeclared or illicit publicity or product promotion, especially on radio or television. 

slush fund

noun
  • Money stored for illegal or dishonest purposes. 

  • Money that has not been hypothecated or dedicated to a particular purpose, or which is used for a different purpose than originally intended. 

How often have the words plugola and slush fund occurred in a corpus of books? (source: Google Ngram Viewer )