There is a lot of misinformation out there, so here is some information I have put together about brake fluid as it applies to your Corvette!
Brake Fluid Ratings, with BP (Boiling Point Standard) in degrees Fahrenheit:
DOT 2 - Forget about it, it is obsolete.
DOT 3 - Glycol based, Dry 401, Wet 284
DOT 4 - Glycol based, Dry 446, Wet 311
DOT 5 - Silicone Based, Dry 500, Wet 356
Dry refers to virgin fluid; wet to fluid that has been in use for a while.
For owners of 63-82 Corvettes, we can eliminate DOT 5 silicone fluid. First of all, it is non hydroscopic, meaning it doesn't mix with moisture. But in the course of normal driving, moisture is going to get into your brake system and cause havoc. By not mixing with the brake fluid, this trapped and highly compressible moisture becomes highly corrosive. Corrosion is one of the reasons every brake caliper on 65-82 Corvettes has either already been sleeved, or probably should be.
Unless you flush and bleed your fluid a couple of times a year, silicone fluid is not the answer. Even dry virgin silicone fluid is more compressible than glycol fluid, so it doesn't work for me, even right out of the box. You can't mix Dot 5 fluid with even a trace of glycol fluid, whereas you don't have to worry about compatibility when switching between glycol-based fluids.
So now we are down to deciding between DOT 3 and DOT 4 fluid. The key number is the wet boiling point, as that is where your car lives. Dry boiling point is only relevant for road racecars, as their fluid is normally changed before every event. The higher the wet boiling point, the longer the fluid will perform well in your car. DOT 3 fluid should be flushed and replaced every year. DOT 4 fluid might give you an extra year. Our Type 200 fluid has a wet boiling point of 396 degrees, the highest of any glycol-based fluid I considered. I concur with the manufacturer's recommendation of a three-year interval between changes.
One last consideration on brake fluid is packaging. The smaller the container the better, and a steel can is much better than a plastic bottle. Moisture penetrates plastic containers, so it is 'wet' by the time you open it.