Steering slop is probably due to linkage (tie rod end, drag link) and not the steering box itself, but you'll need to check everything. Also need to make sure the box is centered properly, the boxes should have near zero play in center, but off-center it is normal to have a small amount of play. If any of the steering parts are worn... replace ALL of them: tie rod assemblies, drag link, idler arm bushings, along with any other worn front-end parts (strut mounts, struts, LCA bushings, ball joints, etc). Then get one alignment at the dealer. If you only replace a single worn item, you end up getting another alignment when the next part wears out, and so on. BTW, don't skimp on brand names, try to get Lemforder for the parts assuming OE/Genuine is not in the budget.

Pretty much only the dealer can align these cars properly, so unless you find an indy MB shop that does alignments properly with the spreader bar, fork over the $$$$ for the dealer alignment.

Don't forget to look at the rear wheel carrier support joints, these are almost always shot, and can affect rear camber. New Lemforder are cheap ($25/ea) but you'll need to improvise or rent the tool to R&R them. There are multiple threads on this topic on this forum and 500E board dot com.