Bruno,

I have two 1992 300s, one an E and the other a TE. I replaced compressor on the E two years ago so I confident that pulley on it's ok. Photo below of TE pulley, you can see the carbon part in the middle is cracking quite a bit. Suprisingly, the bearing is very quite. I could probably use a new pulley but I think I'll wait awhile since bearing is in pretty good shape.

I personally think it's a good idea to periodically take the belt off and spin all the accessory pulleys by hand and listen to bearings. On the M103 engine any of the bearing on the accessories can go bad. I've found bad idler pulley bearings, bad fan clutch bracket bearings, bad tensioner bearings, bad a/c pulley bearings.

When I say bad I mean they make a rumbling sound or you can tell they have no grease in them or are otherwise noisy and do not feel like they should when you spin them.




Edited:
I was at my friends shop this afternoon and he gave me a Mercedes clutch kit for my car which had come in without a coil. I did not want a coil anyway. The special tool also pictured is what he uses to change these out. He said it's easier than a snap ring pliers.

To bad I already had reinstalled my old pulley, but it's pretty easy to remove and with a free new pulley with bearing and spring plate it will not be a problem.