Since you're CONFIDENT in all your preliminary testing...
And you say "ZomeZing" on fuse #9 IS DRAWING 9 VOLTS...
(#9'S CONSUMERS LIST BELOW)
I,Me be turning DMM (Even a Cheap one from HF or Roebuck[on sale] ) to
Amps Scale.
And starting with the Battery ,work Outbound till the culprit is located.
"Doan fergit" the Alternator's Diodes.
How often does Battery Voltage "Go Flat"? How often is chassis Driven?
(Hint: you don't CARE how many VOLTS are being stolen,The Amps are the
true test!)
Oh,Yeah:
http://www.ps2cho.net/downloads/MB%20CD/W124/Main.html
(Section 24 is where your fun begins)