Golf Mk4 2.0 Gti Alternator Clutch Pulley

[Jakg]

My girlfriends got a 1999 VW Golf MK4 GTI.
 
The other day she got an "ALTERNATOR WORKSHOP" message a few times and the battery light came on.
 
Alternator looks to put out the correct voltage, battery looks good, Google suggests that it could be the alternator clutch pulley.
 
I've tested the clutch pulley by removing the belt, locking the alternator with a screwdriver and spinning it - "locked up" i.e. no freewheel in either direction.
 
I've looked online and its suggested I'll need a 33T spine tool and the replacement pulleys seem to use the same fitting (i.e. it's not some bolt you re-use).
 
I've looked at the pulley fitted and it uses a 24mm bolt with a T50 (Torx).
 
I can't seem to find a replacement clutch pulley that uses the 24mm / T50 combination. Does anyone know where I could find one?
Pictures:

[Bellend]

That isn't a clutched pulley mate.

[boneybradley]

This is the alty clutch pulley (and tensioner, I'm basing this on a 2.0 engine and they are £49 by febi)



You can buy just the pulley @ £25 by INA but the tensioners do fail and I sell 1 pulley to every 10 tensioner units

[Bellend]

I think the OP means the actual pulley on the alternator, some models have a freewheeling clutch but this one does not.

Probably easiest to swap the alternator but it could be the regulator or wiring.

[WadGTI]

I have had this message about 3 times or so since I have had the car.

It normally when it is bucketing down with rain on the road. Don't think the alt likes the water 

Never had any issues with charging/noise from the alt.

[h8v]

Is it just that the belt slips when wet?

You could try pouring some water over it as a test.