The holy בעל תשובה

PARSHAS תולדות   The שו"ת מהרש"ל : כ writes, The Chazal of --אינו דומה תפילת צדיק בן צדיק applies only to the תפילת צדיק for his own needs. However, תפילות for others, the opposite is true. It is more beneficial to have a צדיק who is not a בן צדיק  to Daven for you. According to the מהרש"ל, You should seek out a Rebbe that is NOT A  בנן של קדושים.  ברכות of a בעל תשובה are more effective than from a Rebbe who is a  בנן של קדוש