My C220 has 250000km on it and i'm on my third water pump. You've had great luck with yours, and from personal experience, I would just use it till signs of it needing to be changed become obvious. You'll have enough warning of when it needs to be changed, till then if it ain't broke, why fix it?

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems