There are only three parts that go down. The windings will last for years unless you put a screwdriver in them, or try to clean them.

1. Bridge rectifier / aka diodes. Likeliest suspect.

2. Voltage regulator. Unlikely.

3. Bearings. Possible.

The car in question was a 2000 Vauxhall Astra 1.7 tdi with the Isuzu, and the accompanying questionable Hitachi electrics(Japanese firm but made in UK?).

Having been subjected to rebuilt starter motor quality I decided to rebuild my own. Getting the nut off the pulley was hard, but wrapping an old bike inner tube round it got the necessary purchase.

I reckon it'll last another 30.000, as the slip rings are wearing slightly and there is play starting at the outer bearing.

Then I'll replace that item.

It was an experiment, for £22.50, it mey well outlast the car, and it taught me a lot.