this is from the manual for a 1998 C, I think it will be helpful.

Vacuum servo unit check valve- removal testing and refitting.

REMOVAL:
1) Slacken the unit nut and disconnect the vacuum hose from the servo unit.
2) trace the hose back then disconnect it from the inlet manifold/pump connection (as applicable) and remove the hose and valve assembly from the engine compartment.

TESTING:
3) Examine the vacuum hose, check the valve for signs of damage, and renew if necessary.
4) The valve may be tested by blowing through the hose in both directions; air should flow through the valve in one direction only- when blown through the servo unit end of the hose. Renew the hose assembley if this is not the case.

REFITTING:
5) Ensuring that the hose is correctly routed securely reconnect it to the manifold/pump (as applicable) Connect the hose to the servo unit and tighten the union nut to the specified torque.
6) On completion, start the engine and check the valve to servo unit connection for signs of air leaks. Test the opeation of the braking system exhaustively before bringing the car back into service on the road.

Torque figures for 1998 C-230
Servo unit mounting nuts.....11 lbf ft
Servo unit vacuum hose union nut...22 lbf ft
Vacuum pump mounting bolts.....10 lbf ft