Is it Correct to Use MLE Method for GRP Parameter Estimation ?
  Analysis of repair systems usually uses an As Good As New or As Bad As Old repair assumptions. In practice, repair actions do not result in such extreme situations, but rather in a complex transitional one, that is imperfect maintenance, i.e. Generalized Renewal Process. Maximum Likelihood Estimation method is often used for reliability parameter estimation, but is it correct to use it for Generalized Renewal Process 
Sergey Porotsky
stat.AP