[Mxfarm]

Keep in mind the e-brake chambers and the service brake chambers while independent are housed in one unit. The diaphragm in the service brake side is simple to change ( outside of the sealed units ). If your air pressure leaks down while holding the brake pedal down - that's your issue.
-However- while the e-brake side uses a similar diaphragm it also incorporates a rather impressive spring which if released and not contained properly can result in severe injury.