Alternator, Please Help

Ok, I started to drive my 79 300SD with 75K miles and after two days it died. (drove two nights with the lights on 35 Min drive) I went to start the car on the third day and my new 1000cca batt was Dead as a doornail. I charged it (13.5VDC measured), started the car and the voltage output would not get above 12.7 VDC. With the lights on voltage slowly decreased. Also I pulled the connector off the back of the alternator and it had some corrosion. I slipped the connector on and off to try and clean it up I also jiggled it while monitoring the voltage (engine running of course), no change.
I need to straighten it out this weekend. I am very well educated as I have had many American alternators apart and rebuilt them. I have read some previous threads about the brush assembly coming out with the regulator, does this apply to the 79 300 SD? This sounds like a dream come true after dealing with GM regulators. So let me get to the point, should I replace the brushes, regulator, or consider a rebuilt alternator, or am I missing something altogether.

Help!
PeterG