I am a new owner of a 92 XJ with 175k miles. This weekend I want to change out the differential fluid and am looking for what weight and type of gear oil to use. I plan on towing a tent trailer and noticed that the Haynes manual recommends a synthetic oil for the rear diff. The dealer recommeded an additive by I forgot to ask what type. Any tips or recommedations on oils and where to purchase them in the Los Angeles/Orange County area?