Electrical issue: Alternator stops charging when car is in motion

[MC Hammered]

A few months ago when I was driving on the highway the dash trouble indicator lights came on and the voltage drops below 12v as shown in the picture.

When I looked at my setup I saw that there was a small oil leak dripping onto the alternator, so I thought the oil may be contaminating the brushes. I used some electrical cleaner and spray bombed the alternator to try and rinse off any oil buildup.

This seemed to have solved the problem until today. I was stopped at a light and I see the glow of the trouble indicator lights, my voltmeter shows a reading just under 12v. I blip the throttle and no change, I rev past 4000rpm and the indicator lights turn off.

A short while later as I'm cruising on the highway the indicator lights come back on, the voltage drops below 12v again. This time when I rev past 4000rpm the indicator lights remain on until I get home. I restart the car and the indicator lights are all off.

Does anyone have any insight as to what is going wrong?

[MC Hammered]

My friend helped me extract the alternator and along the way I snapped the main power stud. We checked the brushes and they were both worn very short, there was oil contaminating the rotor and brushes as well.

Luckily we had a spare alternator on hand, bolted it up and when I start the car I read a solid 14.0V output vs. the variable 12.5-13.7V range I have been seeing.