140K miles is about right for the brushes. The voltage regulator and brushes come as one unit that is removed from the back of the alternator with a screw driver. Make sure that you disconnect the positive battery cable before you replace the VR. Replacement should take about 10-15 minutes.

The original Bosch alternators are very robust. It is not unusual for them to last 250,000 miles (with one or two VR/brush pack replacements). I would NOT replace the alternator in your car unless it needs it because even the remanufactured Bosch units are relative junk. You are lucky if a reman lasts 5 years.