I recently had to replace my differential on my 540i 6sp sport at 83,000 miles. It had been serviced and fluid changed at 2yrs earlier at 55K miles. No warning except for some very intermittent vague rear-end groaning that sounded like brake pad noise. My panel warning message display showed only once during some stop and go traffic on interstate "Failsafe Engine Mode" then disappeared and all was well. The next day on the interstate, the differential jerked hard and had a loud grinding noise and burnt oil smell. Needless to say, we towed the car to a dealership in Durham NC and had the differential replaced. The dealership was great about the repair !!! The total bill...... well.....not so great. Anyway, we are back in service. Any thoughts on why the differential went out ?? Could it be : Bad Differential Bushings ?? Previous owner doing 'drag-race type' starts ?? Factory Defect ??? Other problems?? And how can I prevent it again ??? Any thoughts would be appreciated here. Thanks in advance !!