Hi: I really doubt you have a problem with DOT3 fluid. There are very few non-standard fluids (Honda PS an exception)these days, although there are different quality fluids. I suppose you could get the name of the fluid used and check with the manufacturer. DOT-4 has a higher boiling point, which means the brakes won't fade out when they get hot (at least not as quickly). Towing, racing, and driving down Pikes Peak are important heat generators. Still, DOT4 isn't that more expensive. A bleed and flush should allay fears, and your mechanic should do it cheap or free. BTW, ATE, the German brake fluid and hardware people, make fluid in TWO colors (same fluid). The idea is that you can tell when the fluid is completely changed because the color is different. I use Valvoline Semi-synthetic brake fluid, which is fairly cheap and mixes with regular fluid, and is DOT4. If your mechanic charged you a hefty sum he should be willing to do a pressure bleed pretty cheap, since he could have read the specs and done it right. Conclusion, even doing nothing is not a big problem.