I checked my charge voltage last week, only max of 13.8v no load dropping to 13.0v with lights and heater fan on full.
Decided to try a new regulator. Mercedes Benz Parts, Mercedes Parts, Accessories
Remove NEG batt lead.
Drive front up onto ramps, chock rear wheels.
Undo 4 x 10mm sump shield screws (had to swap mine for cross head self tappers as the old ones were buggered)
Slide out lower cover.(sump shield)
(Note: If removing alt slacken off belt anr lift off crank pulley, undo 2 wire terminal nuts off alt and the 2 17mm thru bolts and lever alt down.)
To replace regulator in situ follow these inst:
Undo 3 small screws on rear dust cover.
Hold out clips on cover and remove.
Undo 2 cross head screws on Regulator and remove.
Lift out reg.
Mine had worn brushes BUT they were still making contact with a few millimetres of pressure.
Wipe slip rings and contact strip with a rag sparingly sprayed with carb cleaner etc.
Dont worry re wear on slip rings as new brushes will bed in.
If slip rings worh thru you will need a new alt anyway.
Replace reg with the new one.
Note: when ordering Reg quote the Bosch number on the alt as there are 2 types on these, 14mm and 24mm slip ring diameter, mine is 14mm. Both are 14volt.
Replace 2 screws on reg.
Clip on end cover.
Replace 3 small screws.
If you did not remove Alt connect up Neg batt term and start engine. Check voltage. Should be around 14 volts.
Mine was 14.2 with acc on
If you removed Alt, replace 2 thru bolts and 2 wires, refit drive belt and neg term.
Refit sump cover.