I just got my car back from a mechanic after someone interested in buying it booked it in. This mechanic tried to tell me that the diff could last between 500km and 5000km, the buyer was there too by the way. Now my brother also has a skyline, but his diff whine is so much louder than mine, and has been so for far more than 5000km without getting any worse. How can this guy try to tell me that i have as little as 500km left in my diff when I've been told by other mechanics that it could last forever? Is this just a ploy between the mechanic and buyer to get me to lower the asking price? Oh, and how much would a replacement diff?