Any Dot 4 fluid will work fine and all are really about the same, once they comply with the DOT ratings. I've used over the counter auto store brands, including NAPA, for about 35 years, and have only had one master cylinder failure many years ago because I hadn't caught on the the reality of having to change the fluid annually to control water absorption. I also converted one car to DOT 5 about 20 years ago, and still have it (a sweet little E12) and, after an intial hickup (see below) have never had to change the silicon fluid over all that time, because it is absolutely non-moisture absorbing. The problem with DOT 5 is in the conversion process, that is, absolutely (repeat - absolutely) all of the previous moisture from the DOT 4 fluids must be flushed out, otherwise droplets will pool in low elevation areas such as the master cylinder, caliper cylinders and eventially corrode them. Since my E12 conversion in 1986, I had one master cylinder failure about a year later and the cause was an obvious drop of moisture (immiscible in silicon fluid) residing in the master cylinder, scarring the wall. Since that replacement, and an additional DOT 5 flush, the 15 years have gone by without any seal or piston failures of any kind. I love DOT 5, but it has to be carefully installed with lots of flushing, and you should be ready for an incident or two until it settles in over a year or two. It isn't the DOT 5 that's corrosive, its any droplets of moisture that the installer doesn't flush out in the conversion. Bob H.
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