One of my 2011 MC 2.0 diesel's alternator died at 285000km. I found this excellent video for skilled DIYers:
https://www.youtube.com/watch?v=aVvPzwtxdrM
I won't fix mine, I'll get a new one.
A new FoMoCo Valeo alternator goes from about $600 to $1200 depending. 250000km might be a good time to change if you don't want to risk breaking down.
Brushes and slip rings worn out, bearings seem Ok but...