I have seen a Bosch fuel injector cleaning 'machine', but we generally replace the injectors if the mileage is up there. It can be done in the car by using Lubro Moly Diesel Purge. You can run it directly through the injectors rather than dumping the can in the fuel tank. From what I am told, it works pretty well, but as I said before, you can get rebuilt injectors from MB (through Bekkers Import) for about $45/each which is very reasonable. Hope this helps!
'67 250SE Cabriolet
'93 300E 2.8