If I were you I'd just go and bung in a new voltage regulator instead of removing the alternator and then getting it tested.
There's a picture here of the voltage regulator / alternator brush assembly (as I called it then) in Assembly (3) here =>
PeachPartsWiki: Refreshing the Alternator
A voltage regulator swap should be a quick and dirty way of seeing if that is the problem (which I suspect it is with a charging voltage of 12.04V)