Study the ACS. Print it out and discard the pages that don't apply to PP SEL. Its about 115 pages but when you get rid of the parts that don't apply to PP SEL and the flying portion you'll have about 30 or 35 pages of questions the DPE will ask you. Each page has 3 sections for each task (Knowledge, Risk Mgmt, and skills). The DPE will pick his questions directly from the ACS so have a short answer ready for each possible question in the Knowledge, and risk mgmt section. He'll pick one from each section for each task. He will also ask you every question in the "skills" section so make sure you can answer each question for each task. Sounds confusing but when you look at the ACS you'll see what I mean.
Got my ticket in May of this year, and the oral portion was all from the ACS. The PP oral exam guide was the book I used to make sure I had the correct answers for the ACS.
After about 30 minutes of rapid fire questions and answers, the DPE look at me and said "sounds like you know this stuff, lets go fly". Months of studying the ACS, and Oral Exam Guide and it was over in 30 minutes.
Good luck.