If you are putting a new VR in a very old alternator, the slip ring will
eat the new VR carbon contacts.
This is what an old alternator slip ring looks like.
This is a new Bosch slip ring:
If you think the alternator is OK you can take it apart and put it on a lathe or at least file as best you can to get rid of the ridges that will eat the new VR contacts.
GL
J_AZ