Not knowing what kind of vehicle you have, all I can do is guess that it is a load/height sensing proportioning valve.
the brake cylinder is bad or the bleeder valve isn't shut all the way.
Seal in brake caliper is leaking and needs replacement Flexible brake line to the caliper is leaking and needs replacement
brake fluid leaking from a brake drum indicates the brake slave cylander on that wheel is leaking and needs to be replaced you will not see the actual leak with out removing the brake drum
Well if you are refering to the front,then it would be called the caliper,if you are refering to the back it would be called the wheel cylinder....
Rebuild the cylinders on that caliper.
Hub seal is leaking
Brake fluid in a Toyota Sequoia could be leaking from several places. Check the wheel cylinders first as they are a common place to leak.
it is usually the rear brake cylinder that's leaking and needs to be replace on that side.
Axel seals leaking grease on the brake shoes. Wheel cylinders leaking brake fluid. To much brake dust in the drums.
change out your wheel cylinders..
IF you have rear wheel drive it may be a grease seal for the rear differential. Otherwise it is probably a wheel cylinder. Check your brake fluid level. GEt this fixed ASAP- Safety concern. Wheel cylinder, brake fluid.. If it's a rear wheel drive vehicle, it may be the axle seal leaking as well. Hello... hello...
Brake problem. Remove the rear wheel & brake drum, and inspect the brake components. You may have a leaking wheel cylinder or other problem. Also inspect the wheel bearing.