I have noticed over the years that the lifespan of certain aftermarket front end components is very short in comparison to the oem original parts.. I kind of expect this when usimg certain brands of aftermarket parts.
Have no experience with the mercedes aftermarket front end parts though. Other than noticing one centre bar is a lot smaller than the original in diameter and that did make me notice it. I also would not buy and install it even if adaquate. Since the size of most aftermarket front end parts is the same that leaves mostly softer metals as the causitive of any shorter life span perhaps. Some tie rods are really sub standard for example in my opinion.
Aftermarket parts with a really good reputation should not be avoided as the cost savings is pretty large. Just sometimes hard to find that information.