I have had them fail on a car that was only 15 years old. My mechanic said he had seen a lot of them. Now, this car was a Honda, but I challenge you to find a difference between a honda flexible brake line and a Mercedes flexible brake line. I have replaced the flexible brake lines on all but one of my cars (and that one will get it this summer). They all look the same, crimped the same, made out of the same material. In fact, some of them are made by the same supplier (ATE).

EDIT- Mine was a catastrophic failure, not weeping, BTW.