Len, thinking back to belt issues I have had on my E320:
- the first issue was just the belt. Dealer checked other items
- second issue was noise - that was from the idler pulley bearing (replaced idler) Seems your 300D does not have an idler - see video above that replaced the drawings.)
- third was noise again. This time the tensioner bearings (replaced tensioner)
- fourth time noise was from the alternator bearing. I pulled alternator, had it checked and the shop said not to worry. But I put in a reman alternator anyway - R&R not easy job on V-6! Once was enough
For 2nd.3rd and 4th issues, the belt was still good.
Later, the A/C clutch pulley started making a lot of noise. A/C was not working anyway, so I removed the pulley and put in a shorter belt that bypasses the A/C compressor.
Not sure what Jim saw on your alternator pulley? They look indestructible. But they can perhaps be misaligned either due to bad alternator bearings or mount?
Anyway, I am sure you will sort it out!
BTW - The used ABS unit you once bought for me is still working fine. We have stayed in Canada for past 3 winters and it has kicked in a number of times on slippery roads!