The changing your brake fluid issue is the same as the changing your differential fluid issue. Yes there are stories of people going 10 years or 200,000 miles without ever changing the fluid and have no problems.
So let’s just look at this whole thing like a business would maintain a fleet. Cost vs. risk. You do maintenance to reduce the risk of component failure and down time and ultimately subsequent cost. Your maintenance costs have to be less than the repair down time costs. Otherwise it’s more cost effective to leave it alone until it requires fixing.
Not changing any fluid system just increases the risk of corrosion over time and accelerating the subsequent down time.
Brake fluid, as many other system fluids, has an additive package to neutralize the effects of contaminants that induce corrosion. These additives are neutralized during the process and eventually get depleted. Several recent studies indicate that for DOT 3 brake fluid the package is 90% depleted in roughly 3 years.
So, just as engine oil, transmission fluid, differential fluid and power steering fluid have sacrificial additives that have to be replaced and the depletion rate for these different systems vary you have to change them before they are depleted and accelerated corrosion begins.
So! If you think about it and you take a rather selfish hard core business attitude. If you are only going to keep a vehicle for 4-5 years why bother to change fluids such as brake, differential, power steering. However, if you plan to keep your vehicle for a decade plus you would change the fluids to reduce your risk of component failure and higher costs.
Then again if you are a sentimentalist… If you love your baby (vehicle) you’ll take care of it because you love your baby
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