Is this a W126? If it is the chrome have reached the end of their life once they reach about 12-15 years old.
It's likely you'll find the chrome cracking because there's no metal behind it, it's rotten, these rust out from behind.
If it's a corner chrome (one of the side bits that raps around) then it's still available from the main dealer and should be less than £50.
The entire bumper has to come off and I'd strongly recommend you buy a bumper fitting kit, which replaces every nut, bolt and washer on the entire bumper.