WHOA! TIME OUT!!! STOP!!
Replace the voltage regulator/brush holder! Cost $60.00-$80.00
DO NOT replace the alternator! The tip off that you don't replace the alternator is the price of a new alternator. the only time you replace an alternator is if you have a failed bearing, even then a Bosch shop can repair it for under $100.00!
Most shops don't offer to simply replace the Voltage regulator/rectifier/brush holder module since most grease monkeys prefer to rape you and your credit card for the price of a new alternator plus labor!
VW alternators come with replaceable VR/Brush holders that wear out BUT are easily (relatively) replaced. reference item #4 in the diagram below...
You can easily replace the plug in module in the parking lot with some fairly basic tools.
VOLTAGE REGULATOR NEW
(Compatible with OEM part number: 038-903-803-EX)
List Price: $87.59 :: Impex Price: $65.53