Hmmmmmm.............ABS doesn't use interior CAN which would be the affected network if a DCM failed. HMB also says several other warning messages are displayed at the ICM, which are usually engine CAN related. I'd suggest taking a look beneath the R/R seat and check for water at the rear SAM. W220's are notorious for clogged reed valves which allows rain water to enter the cabin via the fresh air door, eventually working it's way to the SAM. It only takes a minute to remove the rear seat bench so there's nothing to lose.

If everything is dry I'd suggest running a scan with SDS. That should help narrow down the list of suspects pretty quickly...........