Not saying these ARE what happened, just possibilities...
Brake lines are a combination of metal tubing snaking around the bottom of the car, these in turn connect to flexible rubber hoses going to the brakes at each wheel. Those hoses can and do age with time especially if subjected to harsh chemicals. The typical failures are:
- Cracks/splits that let fluid leak when the brakes are applied (creating pressure in the fluid).
- The brake hoses are built pretty much the same as other high-pressure hoses: the rubber hose ends terminate in crimped connector that tightly squeezes the hose around a central metal tube that is part of the metal flare-nut connection fitting. When old, the rubber dries up a bit and shrinks so that squeeze isn't tight any longer and you get a leak there. This is a common leak in air conditioner hoses as well since they are subjected to engine bay temperatures and flexing as the engine rocks side-to-side under hard acceleration.
- The rubber hose gets soft and expands like an inflating balloon when the brakes are applied. This is not easily spotted by eye unless somebody else is pushing on the brake pedal... and even then it is easy to miss as the hose expands just a small amount.
Any of the above failures reduce braking action as the pressure is being wasted instead of pushing the caliper pistons into the brake pads. Loosing fluid is even more problematic and will lead to the brake light being ON as your car is experiencing.
BUT... and this is where a shady repair shop can create work for themselves - simply loosening the fitting between the metal tubing and the rubber hose connection introduces a small leak. That will lead to fluid drips below the car when the brake pedal is pushed and wetness around the fitting. Brake fluid leaks are easy to spot as they'll be wet; sometimes the brake fluid shoots out in a stream/spray getting all over the place. If the leak is at a fitting (i.e. you can see where one would apply wrenches to tighten/loosen the joint) then it could easily be a shady repair shop loosing that fitting.
If fluid leaks where the crimped metal piece ends then it could be old/dried-out hoses that really did need replacement.
If the leak is at a cracks or split in a rubber hose... look at how many cracks and splits exist in that hose and in the other brake hoses at each wheel... they should be wearing at a similar rate so if one looks bad and is leaking while the others don't show as much cracking/splitting then that too is an indication of a shady shop sabotaging your vehicle.
In theory the metal brake lines can get bent/damaged creating leaks - just like bending a soda/drinking straw tends to lead to leaks. They can also rust if the surface treatments have been worn away or destroyed by chemical exposure. Rather rare though on modern cars.
Most shops that find things during an inspection would put the car on a lift and show you the evidence. They can "plant evidence" too by simply wiping brake fluid onto joints, hoses, etc. to say "see, here's the leak." Similar tricks have been used to falsely show all sorts of faulty car parts: spraying simple oil onto shock absorbers near the shiny metal shaft to imply the seal around the shaft is leaking so the whole shock must be replaced is another common trick. One of the chain tire/suspension shops decades ago in California got caught doing this at multiple locations and was heavily fined.
So what should the OP do? Leaking brakes - due to actual failures or shady shops loosening fittings or cutting hoses - is nothing to take lightly. Adding the appropriate brake fluid to the brake reservoir under the hood (the owners manual will list the proper type) IF THERE IS STILL SOME FLUID IN THE RESERVOIR is the first step and could make the car driveable to a different shop. But, and this is the risk, if the fluid level in the reservoir got too low, air would have been sucked into the brake lines so the brake system would need to be bled before the vehicle is driven. Not knowing what the OP's situation is, I would suggest a tow instead. Even if there was enough fluid in the reservoir to cover the pick-up port going to the brake master cylinder, that fluid sloshes around while driving. So the port can suck in air at times. Risky. That's why the reservoir has the "MIN" tick mark in fact - that tick mark is "enough fluid exists to compensate for fluid sloshing during cornering, acceleration, deceleration, and going uphill/downhill to make sure no air gets into the system."
Repair parts: the rubber brake hoses should be available from the dealer and some auto parts stores. They aren't high-tech parts that would be dealer only. The metal brake lines would probably be dealer only simply because they rarely fail (so parts stores would not want to carry inventory) and are physically large and fragile - a miserable combination for parts stores too. Any decent tire/brake shop or the dealer can do a proper inspection and repair. Many brake shops can custom-build the metal hoses; they are just metal tubing with gentle bends and flare nut fittings on the ends after all. Even the rubber hoses can be rebuilt: the crimp is cut apart (like a banana peel), then the old hose is removed from the end fitting. A new hose, and a new crimp shell, complete the rebuild. Exact same process as used on air condition hoses.
mike c.
