The voltage regulator may be purchased from this site. Look for the "Buy Parts" icon more towards the top of your display screen.

As Larry Bible stated, it's on the backside of your alternator. 2 phillips screws are removed and out it comes.

Unless you weigh 60 lbs., it will help to elevate the front of the car some. I find ramps useful. Underneath the car you may find a large shroud that will need to be removed. There may be from 4 - 8 small metal screws with a hex head(8mm in some cases). Those come off to remove the shroud. With it out of the way, you'll see the alternator on the passenger side from down below.

New brushes on the voltage regulator are pretty close to 1/2 inch long.

It takes longer to setup for this job than to pull and replace the voltage regulator.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"