I'm surprised more people don't lower their ML's.

Don't know why four new lowering springs wouldn't do the job.

I'd go to the Brabus site and see what packages they offer for lowering ML's
Then I'd go to H&R's site and see what springs they offer for lowering.

I'm not familiar with the ML suspension, if it has Airmatic or electric shocks?

But whatever reps you talk to at any of the spring manufacturers, explain you don't want to stiffen the ride quality at all, just lowering.