This happened a while ago, but found the photo today. Went for a nice long ride and towards the end, the front brake was feeling "spongy". Still worked, just had a soft lever. Looked at the pads and they were thin, so I changed them out. After the pads were done, pulled on the lever to pump it back to life and nothing. Right to the bar. WTF? Tried to bleed them and would not pull fluid. Couldn't pull with a vacuum or push with the lever. I pulled the master cylinder apart and this is what I found.
The return spring was in 4 pieces. (New spring on top of the pic) Never seen that before on cars or bikes. Oh, and the fluid looked like pancake syrup. The cups were actually in OK shape, but rebuilt the master and it bled first try.
My theory is that the spring could not return the piston back far enough to allow more fluid in giving the weird feel to the lever. I guess even XR brakes don't quite last forever.