Excessions article on junk hands (part of PT series) is very good. It helps you pinpoint which hands you might be overplaying (for me it was K10o).
For me the best way to find a leak is not so much a particular stat, but rather looking back over the top 5 winning hands and top 5 losing hands of a session. Do this for several sessions and you can pick up a pattern. Are you losing lots with TPTK? Are you not respecting reraises? Etc.
Tim