Right this is a fun situation .... My 2.2 cd has been great after the repairs I have done so far, Tonight she decided that to work is a BAD idea

As we were driving along I had to stop and leave the car running with the hazards on due to a stray dog going mental in the road, After 10 minutes or so the dash lights and abs light were flashing along with the hazards and any extra load like heaters and radio made the car idle badly!

I took the car straight to my dad's house as he has one of those magic electrical tester thingy mabobs on sidelights only as everything else was causing issues. Voltage reading while running was 11.4 volts at the battery with engine idling and everything turned off

turned car off and changed battery for a fully charged one and same thing was happening ... When first started the voltage reads 13.4 volts and rapidly drops to 12 volts with no load! Took the alternator off and dismantled the brush pack job, gave it all a good clean (it's a Bosch 100A alternator)! Refitted to the car and the same issue remains

I have to be inclined to think that the alternator is dead but I just want some second opinions before I go throw cash at the breakers for a new unit. If it's just that brush pack thing I can get one from a zafira but I don't want to buy parts I don't need.
All earths tested as good and no battery light comes on when driving (this does work though)
Thanks in advance Graham