great to get to the bottom of the fault you aren't on your own with finding aftermarket part troublesome i will not use non genuine parts as too many of the aftermarket parts just dont work or create more problems.
i know its dificult with rover but i have had this on numerous jobs the last was a rover sterling no charge from alt recomended new one
had a call to say still had problem went back same again replacment alt faulty did this 3 times before i took the altenator to my local reconditioner who repaired the NEW unit and i went back and fitted it.
however the original supplyer would not pay my labor or the cost of the repair