Sorry it has taken me so long to respond. What with my wife's insistence on doing the Christmas shopping and a broken water line, there just hasn't been a lot of time for MercedesShopping.
The manual's description of testing the brake vacuum cylinder is complicated. It entails use of a vacuum tester, a pressure tester (which is inserted between a brake line and a caliper), a pedal pressure tester and a self-made tool to be inserted into the vacuum line leading to the vacuum unit allowing for connection of the vacuum tester. Overall, I'd say the MB manual procedure is impractical for the DIY.
Perhaps someone in the forum can recommend a simpler, more practical procedure for a DIY to accomplish this job.
Regret being the bearer of bad tidings. Hope someone else can help.