2005 Boxster Brake

[hengelking]

I have bled my brakes and they now very solid but still are not strong when stopping at slower speed, I notice it mostly at slow speeds, like stop and go type traffic. I suppose the only possible explanations are a bad master cylinder, bad vacuum brake booster or a vacuum leak. I am leaning toward vacuum related. Any easy tests to confirm or narrow the possible reasons for the weak brakes at slower speeds. How can I find a vacuum leak?