I'm not sure how accessible it is. I've done this in the past with a couple of my old Audi cars and I was lucky enough where I had just enough room to replace the voltage regulator without removing the alternator. There are a few part numbers but I'm not sure which one you will need 028 903 803 E, 00A 903 803 A, 06B 903 803 B as I got these numbers
from this site