no reverse on 560 sel
No adjustments will help. Can be the infamous 'B2' piston failure, or a failed seal on the reverse clutch pack--either the one on the input shaft to the clutch pack, or the piston seal ring.
Since this is the first thing to come out after removing the front pump from the tranny, rebuilding just the reverse clutch is easy (parts cost less than $50) labor for the clutch rebuild only is maybe $75. Big hit is removal and reinstallation of the tranny (6-8 hrs)
If you do not have the connections with a good MB tranny tech to do just the clutch, most relaible thing is to get MBZ remaned tranny installed or have it rebuilt by a MBZ tech that specializes in tranny's.