If the ring and pinion are worn smoothly all the way around, that is no chips,spalling or missing metal. What you are looking for here is a nice even wear pattern. If this is the case, then the differential will probably need new thrust washers, spacers and a new crush sleeve for the pinion gear. This is necessary to reestablish proper backlash and clearance between the ring and pinion. This type of work requires micro dial readout gauges and the all the hardware to set up the rear end for measuring and adjustment ie end play backlash ring gear runout, etc.... It is possible to improve excessive backlash due to actual wear between the gears by adjusting clearances and the like, however due to some of the inherent physical properties of hypoid gear sets, it is likely that you may never get the noise level back to new, but with a good man at the gauges, it should be a whole lot better than it was. This type of work is definitely not for the weekend warrior unless you are really patient and understand the geometry of the gears inside that case. BTW, you're right, a differential is a differential, some fancier than others, but they all share the same basic components and function, so if you know a really good mech who has experience with rear end work, let him take a look. I have a friend who sets up pro stock drag racing cars. This guy knows rear ends like the back of his hand and... he doesn't work for MB. Look around,but be careful, some people will try to sell you a new car in the process.