OP: I don't have the attrition rates but can assure you that most people who get into any of the programs make it through. That said, there is attrition at every step of the way for everyone: grades, attitude, desire, and conduct. I would guess that in the end, the highest attrition rate for NROTC, PLC and OCS would be time spent in Quantico during Bulldog/ OCS or whatever it is called now. During this critical training/assessment phase Officer candidates are evaluated by instructors and peers; experience a tough training evolution, and face lots of personal challenges. Attrition can come from bad attitudes, lack of desire, poor performance, bad conduct or physical limitations.
If you have got what it takes and have the desire to become a Marine Officer there is no need to worry about attrition rates.