Well, I'm sorry that you do!

You may or may not know that Beck/Arnley has never been and is not a manufacturer of the parts they sold, they are a re-boxer of parts they sell. While there may be some listing somewhere that claims the parts you have are "for" a certain application, it seems that you've invested in believing some unverifiable sales pitch rather than your own lying eyes in this case.

The original equipment is completely different design (multi piece), are you for the sake of some dollars assuming that the engineers at MB are less than competent and that the second tier parts buyers at Beck/Arnley are superior in their reasoning and understanding of the differences in the design characteristics of the simple ring vs. the OE multi-part oil ring design? On the surface it seems that's the reasoning being applied.

The rings you have bought might fit within the parameters of the original physical specifications but there is no question that the design and function of your Beck/Arnley parts are nothing like the original MB parts that have lasted for hundreds of thousands of miles, right?

My contention is that your Beck/Arnley parts might not induce a complete failure instantaneously, but it is virtually guaranteed that they can not and will not perform as suitably as the correct design and specified original parts per MB.

It is interesting that you are arguing that the expander spring is not for your application and was incorrectly included in the boxing of these parts, when your own description and photo show that the original parts had an expander, why have you decided that the inclusion of the expander is incorrect and not concluded that the oil ring which is obviously a completely different design and a completely different physical dimension is not the part incorrectly included in the box of parts claimed to be appropriate for that engine?

Your original post asked about the expander you have "what is it for", it's for use with an oil ring the same specification as the Original Equipment, a thinner ring that is designed to function with the expander supporting and assisting its design function and operation.

The oil ring included in that set of parts while meeting the most basic requirements of circumference and thickness which allow it to fit into the dimensions of the groove in the piston, does not follow the design specifications and functional specifications of the original parts, of that there is no question whatsoever.

It's your engine and your choice, I was simply responding as to what the potential overall effect of using parts that are dis-similar to the originals particularly in a fairly critical application. Good luck!