Finding Vacuum Leaks

Hi

I have a 1995 C280 witht the master vaccum pump cylcing on and off and there's a leak in the vaccum lines behind the dash - this is what a MB dealer diagnostic test said. Anyhow, once I pull that dash out, how can I find the leaky lines - do I use a stethoscope or blow smoke in lines or use vaccuum line tester. Also, where can I get the testing quipment that I will need. I would appreciate if someone could tel me the cheapest, most economical way to find the leak.

Thanks,
Troy