The dealer says I need to have the brake lines flushed and fluid replaced at 40,000 miles rather than adding brake fluid to the master cylinder as it is low. Is this valid or $150 to the dealer?
Brake fluid should be changed every 3 years as it absorbs water from the air. That water corrodes the brake system from the INside so get it done but you don’t have to use the dealer for this.
Since this car uses the ABS system to brake the car after regeneration has been completed, you should not be cheap on its service. Since the ABS system is very expensive, a few dollars spent on flushing often is adviseable. I would flush the brakes more often than 40k.
What the others said. Also, why is your fluid low? Brake fluid doesn’t evaporate. If it’s low, it’s either because there’s a leak which needs to be fixed, or because the pads are worn down and need to be replaced.
But you were wise to ask for outside advice, especially since it’s a dealership instead of a “Trusted Independent Mechanic”. (Some dealerships are trustworthy, but if OP is asking then s/he does not trust this one.)
Based on similar advice I have gotten here, I have my independent mechanic flush my '04 Camry’s brakes every 30K miles or so (that’s about four years). I think I pay for about 1 hour labor, plus the break fluid.
You might save a little money going to an independent. Since this maintenance is important but not a crisis, you have time to shop around. And that will help you find a trustworthy (competent) independent mechanic for out-of-warranty service.
Your owners manual will list all required services and their service interval. Many manufacturers do recommend a flush every 3 years or so for vehicles that have ABS.
In your owners manual, there is a page dedicated to checking your brake fluid. It recommends that you DO NOT add brake fluid when it is a little low. When it gets near the the minimum, you need to have your brakes inspected as that is an indication that the brake pads are about worn out.
If you are only a little low, don’t do anything. If you are near minimum, have the brakes inspected before you do anything else. The worse case is that you are near the min, you allow the dealer to flush the system and then he tells you that you need new brakes. Of course after you have new brakes installed, the system will need to be flushed and bleed again so you pay twice.