The Pc (P3) line from the compressor scroll to the Pc filter does not appear to be the one mugsy has mentioned.
mugsy wrote:
The cause appears to be a cracked air line between the governor and Fuel control unit
Although the Pc line has been a problem over the years.
Vfr: The Chadwick test is a vibration analysis check. Chadwick is one brand name of the test equipment that is commonly used and is also used a lot for rotor track/balancing.