white46

If you belt and pulleys starting to squeak, there is what you need to know before starting to replace.
This post is for your own reference, and parts were found from 2008 C300 with m272 engine. Not sure on any other models, so please do your own homework.
All below information is what I gathered on internet plus what I've worked on my car.
Parts numbers were taken from https://nemigaparts.com/cat_spares/epc/mercedes/

Here is what belt diagram looks like.


#2 Tensioner Pulley - Part# 2722000270
Most of time tensioner is fine but pulley goes bad, but since there is no separate part # for pulley itself, you need to purchase whole tensioner assembly which costs $70-$80.
In this case, you can go with aftermarket pulley with following part # for about $15.
1. Dayco 89007
2. ACDelco 38006 -> what I used
3. Gates 38006

#3 Idler Pulley - Smooth - Part# 2722021419
About $20-$30
You can use following aftermarket pulleys.
1. Ina 5320539100 (OEM)-> what I used
2. Dayco 89514
3. Gates 36372
4. ACDelco 36372

#6 Idler Pulley - Grooved - Part# 2722020000 and 2722021019 comes with hardware. 0002020919 doesn't come with hardware.
Interestingly there are 3 MB Part # you can use for this pulley. Everything is is about $20, except 0002020919 which is about $5.
1. Litens 532052610 (OEM)
2. Dayco 89095
3. ACDelco 38099
4. Gates 38099
5. Ina 0002020919 -> what I used

Serpentine Belt - Part# 0039937296 about $25
1. Gates K060947 (OEM)
2. Dayco 5060945 -> what I used

So in total, you can replace all 3 pulleys and belt for under $100.