See the below file for maintenance procedures and information for the CPS-20M, CPS-20M-HC20, and CPS-20M-P3K for the 6270A and 2271A pressure controllers.
See the 6270A Service Manual for the part numbers
See this article for CPS-20M Test Port o-rings, CPS-20M Test Port O-Rings
Note that a much quieter muffler is available to replace the original small metal filter. If you have a CPS-20M with the original metal filter,contact Pressure Calibration Technical Support by the link below, Submit a request