The troubleshooting section o n the CD will help you but it is dificult at best to work with.

Try to isolate the positions on the acc controller that you hear the leak in. Then check the manual for what valves etc are open or closed in those positions. Then you will propbably have to pull the center console and dive into the mess behind there.

I removed my seats as they only have four bolts holding them and it made teh center console removal much easier.
Once you get int here you may find that the leak is just coming from a broken rubber vacuum connector in whioch case it is extremely cheap to fix. You can run the acc with the console out and then get our ear down there to try to isolate the cause of the leak.

One other thing to try is running the car with teh acc in the offending setting then shut the car down and you should get a clearer location of the leak for the brief moments that it still leaks before you lose all vacuum.

Good luck.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique