Michael, I have serviced thousands of Mercedes 6 cylinder engines, I have NEVER replaced a timing chain on one. I have done valve jobs, over and over. I would bet that what caused your breakage wasn't the rails, although it may have appeared that way.
My bet is something else caused this.
I have seen failure of timing chains because of things like camshaft seizure and soforth, but I have not done a preventive replacement on a 6.
And just FYI, the 6 PASI has is different from yours. His has a double roller chain where yours is a single roller.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS