Worn generator brushes on one side only… extremely fast

Update: I replaced these new unbranded brushes with my old bosch ones, cleaned the commutator (fine grit sandpaper + contact cleaner) and all seems good now. No generator red light, no visible wearing of the brushes.

Getting a hold of decent carbon brushes is a mission these days as the new ones are cheaply made and not compressed under as high a pressure when manufactured. This then makes a soft material that will wear quickly.
I would, however, check for play in the genny's front bearing. This is cause the constant downwards pressure of the belt tension will cause the bearing to wear and pull down.

psimitar said:

Getting a hold of decent carbon brushes is a mission these days as the new ones are cheaply made and not compressed under as high a pressure when manufactured. This then makes a soft material that will wear quickly.
I would, however, check for play in the genny's front bearing. This is cause the constant downwards pressure of the belt tension will cause the bearing to wear and pull down.

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I would agree, the combination of soft brushes and a worn bearing could cause the lower brush to get chewed very quickly.
If you find the bearing is worn, replacing it yourself is a worthwhile job, (especially if you buy the bearing from a general bearing supplier instead of any "Classic VW" parts specialist), but you will have to remove the generator from the car, to dismantle and get access to the bearing.
I recently replaced noisy rough bearings on my Beetle alternator with genuine SKF bearings from: simplybearings.co.uk , just over £13 for the pair.

I had the gen out of the car in the very recent rebuild, and there is no play in the gen bearings. I did put the original lower brush in, and everything seems alright. I just guess the replacement brushes were indeed crap.

Clean smooth commutator + good hard brushes will last a long time compared to rough dirty commutator + soft replacement brushes.