only when they get a lot of mileage or heavy loads or if they are driven "hard". my 97 had 337kms on it when I traded it, original tranny/engine
im not complaining , my safari is rounding about 430,000 miles and has a slight slip, but i just throw some Lucas transmission fliud in it and it's fine. it's a thick blend but works amazing, just don't overfill.
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