Had this on my partners 97 om606 , the overrun pulley starts to seize up and eventually winds itself off the alternator shaft.
You can get the alternator out from above , it’s quite a few twists and turns but it does come out.
I had to clean the alternator shafts threads up slightly but a new overrun pulley fitted back on ok.
These overrun pulleys only drive one way so when you rev engine high and quickly drop the throttle the alternator can still run at speed, once they start to go bad then you start hearing odd clicking noises.
When they are seizing up internally then when you switch off the engine the kick back as engine stops turning ( there’s that little bit where it turns backwards slightly ) helps to unwind it off the alternator shaft.

Murkybenz - so when you took out the alternator from above, did you have to disconnect and hoses, etc.?

__________________
Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles

On my 95 E300D, when I installed my ' one way ' pulley, the alternator shaft was shorter than the pulley was wide. I found a large set screw and tightened it against the alternator shaft. This locked the pulley to the shaft. Same principle as a jam nut. I do not believe my pulley can be loosened/removed until that set screw is removed.

I think for alternator work I used my oil change ramps to gain working height to access the alternator mount bolts. Even though the alternator was still working I had it rebuilt by a local shop with new bearings and regulator.