My first point would be that the system is designed such that a total failure of all systems will not affect the brakes. In other words if you just pull the two small vacuum source lines from the large power booster source line and leave them open the leaks should be small compared to source vacuum and the booster should see sufficient vacuum to do its job.

Since you mentioned the brake problem, I assume that your source vacuum is POOR! This needs to be the first step. With no leaks, vacuum in the line to the booster should be over 20in. Vacuum should drop maybe 5in with a brake application but rapidly recover as the pedal is held (one second plus or minus). This should be done by removing the supply lines and attaching the gauge to one of them (plug the other). After verifying the system vacuum proceed with each system one at a time by reinstalling the lines to the booster line. The single line branches and has check valves, at the first branch only hook-up one side (plug other). Do this for the four possible directions the vacuum goes. Brown = fuel shut-off, Green = A/C, Yellow = door locks and Black = cruise control.

I would start with the Brown to verify that important system. Next add door locks and if they have no history I would replace all three door chambers (they all should have failed by now). They can be purchased for a fraction of the MB list of $92 (we would sell 3 for less than $150).

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician