After 225k miles it appears that the ring/pinion gears in the rear diff are shot. Loud clunk, clunk, clunk noise coming from the rear under moderate acceleration, much worse going uphill.(The problem has grown steadily worse over the last 1k miles to the point where I don't want to get on the road) . The rear stepper motor was replaced by VW when the car was much younger, but a rear end binding problem (noted especially after traveling over speed bumps) was never resolved. My VW tech's workaround was to quickly switch the 4x4 mode control from 4 High to Low and back again. This worked to stop the binding, but over the course of time major damage was done to the rear end. So my question for those of you that know about 04 Rear Diff /lock issues is that if I am lucky enough to find a salvage rear diff with lock, how can I be sure that its the right part for my Touareg? Correct Ratio? Are there markings on the unit I should look for, or cross reference lists by vehicle year? The savage guys say that VW used the same unit for a couple of years. Given the mileage on the car I can't see spending $4k at the dealership. Thanks in advance for whatever worthy info you can contribute.