Mercedes: Fuel Injectors, injector system, fule

Question
How often should I clean the fuel injectors on my 190E 2.6 Mercedes? I have 140,000 miles and have never had the Injector system cleaned.
Is cleaning the fule injectors something I can do myself?

Answer
I replace them every 150,000 miles for MPG and performance reasons.

Many shops add a can of system cleaner to your fuel tank.

A leaking injector can cost you engine and catalytic converter damage = it is cheaper to replace them, and reclaim MPG/performance that was lost.