Here's yet another opinion on the subject. At 100K miles, all four of your shocks are on borrowed time. Leaks, or no leaks, are not the criteria for replacement. It's the internal parts that wear out and they do so slowly so that it all sneaks up on you. As to Koni's, I say no. I replaced Bilsteins with Koni on a past Mercedes and ruined the ride. And, as to Bilstein HD's, on the other MB lists I have seen plenty of posts from owners who fitted them and found them too stiff.
Buy the "comfort"version Bilstein and not from your dealer. I replaced the shocks on my C280 and paid about half what the dealer wanted from another source.