Off topic: Time is also a big factor to keep in mind. For example, when a bought mine, it had only 67.000 km, but 12 years. When the rear diff was drained, around 300 ml of black sludge came out (minimum maintenance from the Italian ex-owner, just engine oil every 2 years and apparently one transfer box oil, but a strange yellow one). Personally, I believe that 5-7 years is more than enough for any lubricant on vehicles. Needles to say that in my case, all the fluids and belts from the car were changed before good use.You wont change autom transmission oils more than maybe 100tkm intervals. Same with transfer box and rear end oils.