Dot 3/4 and 5.1 brake fluid is hygroscopic (attracts water vapor when exposed to air), so that's why you change it and why you need to avoid having stored brake fluid exposed to air.
Having said this, it is going a bit overboard to throw away new brake fluid in a sealed bottle just because the it has been momentairly exposed to air. If the cap seals tightly, the amount of moisture the brake fluid can attract in the small parcel of air in the bottle is exceedingly small. I suppose it might become significantly if you opened/closed the bottle tens of times, but under normal circumstances, there is no reason not to continue to use brake fluid that has been kept in a airtight bottle.
I don't know for certain, but I'd be amazed if VTM4 fluid was hygroscopic. Assuming that it is not, the shelf life of the fluid should be very long - virtually indefinite - provided it has been stored in a reasonable place and kept in a sealed container.
Don't go overboard when you hear things on the net - this is not the space shuttle we're working on here, or even a Ferrari. It's a common everyday car and requires only reasonable care.
- Mark
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