I noticed my Brake fluid level was very low the other day, and that there was paint removed from below the power brake unit?

Also where the fluid has leaked it has eaten the paint away from the sides of the engine bay.

Is this a failed brake master cylinder? what could be the cause of this?

 

yes it is. the seal on the piston inside of the master cylinder is faulty. its has probably shrunken with age and use. this is pretty normal. the bad thing is that if you or the previous owner did not replace the brake fluid every year or so, water/moisture has probably gotten into the master cylinder and perhaps the cylinder wall is rusted. you can either replace the unit with a new or rebuilt unit or rebuild it yourself. either way you'll want to bench bleed it to ensure faster bleeding. without bench bleeding, it is often difficult to bleed.

 

Yep, classic BMS failure symptom. Hopefully, it hasn't also damaged the booster. Brake fluid is destructive stuff.

 

Hey DD already knows haha. Yes I had to replace my booster because of a leaky BMC. It is pretty rare to happen I believe but it happened to me and it took me a while to figure it out myself. Even mechanics didn't understand my problem. All of my posts are in a thread titled "disappearing brakes?"

Make sure to use rags and towels to catch any brake fluid coming out of the ports or lines usually to prevent fluid dripping on your paint because like said earlier.. its nasty stuff. Other than that replacing your BMC and bleeding and bench bleeding should be quite easy. Good luck

 

Could be that a previous owner dumped some fluid in that area when filling the resevoir. But if you are loosing fluid now, then that is the most likely cause. To be certain though, I'd also suggest checking inside the wheels to see if any fluid has collected there, which would indicate a bad caliper or cylinder. The fluid will usually collect inside the wheel (in the back side) and build up a lot of dust and dirt as a result.