DOT 5 fluid (silicone fluid) )is the only brake fluid that is not hygroscopic (not hydroscopic), like DOT 3 and 4 which are hygroscopic, that is, they attract and retain moisture within the molecular content of the fluid. I too, have poured both in a clear jar and sat it on a shelf for months and saw no interaction between the two. I would not recommend mixing it in a car's brake system though. Its best to do a thorough flush and refill, and even better when the system is being rebuilt with new rubber parts installed.
Bob J
1961 300G convert running DOT 5 silicone fluid for 32 years.
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