My left rear brake light is out and I am losing a lot of brake fluid.
Sounds like you have multiple issues going on. Brake light bulbs going out is a common thing. Most are fairly easy to change with a few tools. The thing to watch for is to make sure the bulb socket is not damaged. A lot of times they get burnt or melted. This can cause a connection issue and even if the bulb is good, the tail light may not work. The fluid can be coming from several places. A cars brake system has rubber hoses, calipers, wheel cylinders, and a master cylinder that can all leak fluid. Since bakes work off of hydraulic pressure, this can be a safety issue. I suggest seeking the help and advice from a qualified mechanic, such as one from YourMechanic, to help determine what needs to be done to properly repair the brake fluid leak.
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