I just brought my car in for an oil change (29450 miles) and the dealer inspection found the rear diff lube was 'showing signs of wear..discoloration' . I'm not all that concerned about replacing diff lube, but the estimate is totally shocking. I was quoted $176 for this service. That includes $41 in service (about a half hour which makes sense), and that includes $122 in parts! Huh ? $122 for about 1.5 quarts of gear lube.?Is this some really special lube and if so why would it need replacing at under 30K miles? Royal Purple is the most expensive brand I can think ok and that runs $16 a quart. Am I missing something here?