ML430 - Serpentine belt issues

[mbz16v]

I recently purchased a 2000 ML430 which appears to have been well cared for, but something occurred this evening that requires immediate attention.

When I started the vehicle I heard a faint "clicking" noise, but we weren't at home and I couldn't (wearing a suit) examine the engine.

We came to a stop halfway home and the noise had become much louder, but now sounded like a flapping noise. I opened the hood and immediately could see where the noise was originating...it looked like something was tangled in one of the pulley wheels on the serpentine belt.

I immediately shut off the engine and had a clear view of the issue...the wheel in question had an outer ring (it looked like it was rubber) that was separating from the rest of the unit.

We had to continue home (ten minutes on the highway) and I wasn't surprised when we arrived that the "rubber ring" had completed it's separation and was no longer there...the noise was gone and only a faint smell of buring rubber alerted us that something had happened.

I've done extensive engine work on my 16v's and C280, but I'm far too busy right now to work on this task (assuming it might be a big one). First, I need to determine what exactly occurred and why. Second, I need to know if this is something I should tackle myself. And third, I need to know how much whatever needs to be done should cost if I bring the ML in for service.

I'm attaching four pictures for review...two from each side of the engine bay (regular view and closeup).

Any help would be appreciated.

Thanks,
Andrew