It also depends on if you would fit a like for like replacement or go for an uprated higher capacity alternator. If uprating that would always be my recommendation but if fitting like for like then you might as well repair as long as you are confident enough with the process. Or do both a new regulator is cheap enough as long as you don't need the vehicle as a daily drive you could try rebuilding and if it doesn't work then replace and you have only lost a couple £ for a new regulator or the other way around, fit a replacement and then rebuild the old one as a spare.
