Just a thread resurrection ....a few years on. I've had the Boge on my RRC reconditioned by ZF in Germany - they own Boge now. They do a heritage programme - it wasn't cheap (about 900 euro), but it's restored the original self adjustment. Cost depends on how shagged the original item is.
Try looking here - ZF Tradition - ZF You're looking for the Nivomat shocks section. They used them on old Mercs as well.
Good luck!