Alright guys, long story short I was commuting on my mountain bike (dark, about 5am) and hit an iron gate someone had left open across the cycle path. The impact was concentrated directly on my rear brake lever, as you can see in this image:
I was traveling at a fair rate of knots, enough to throw me over the bars and unfortunately I believe it has damaged the brake internals. This video: VID attempts to show what my problem is. In the clip, I am applying light pressure to the lever and rolling it back and forth. On the forward movement of the bike, the lever sinks very slightly, and this repeats until it touches the grip. Pumping the lever reverses the effect. As you can see after the first demonstration, applying pressure when the bike is stationary has no adverse effects and this is what confuses me. There are no external leaks, no parts missing.
Anyone got any idea at all what could be the problem? I'm expecting the worst (master cylinder damage) so don't hold back on your thoughts.
Please excuse the dressing gown and bare feet in the video