1997 C200 Estate: Steering Arm Replacement

The garage has advised me that the offside "steering arm" on my 1997 C200 estate is exhibiting excessive movement and needs replaced. This part is what I would have called the track rod. Apparently this part is not available separately and the entire assembly has to be purchased and replaced.

Can anyone kindly tell me:-

1. what is the correct name for this part; and

1. is it easy or difficult to replace?

Thanks.