We start out with things looking bad, but not absurdly so. There's an evenly-distributed film of crud that coats the outside of the chain links. So much so that the rivets have become almost invisible.
Not a good way to treat a $200 DuraAce cassette. Whether steel or titanium, cogs wear much more quickly when subjected to an abrasive grit like this.
This is as bad as it gets. So much gunk on the chain that it actually deposits on the front derailleur as it scrapes against the chain. The amazing thing is how well the bike continued to shift, despite so much grit & grime on the drivetrain.
OK, so that last photo isn't as bad as it gets! This is the back side of the rear derailleur, showing an extraordinary accumulation of crud.
