I had exactly the same problem, until I broke the right footpeg bracket. When putting it all back together I could not get the brake lever back on the spindle of the bracket. I pushed, pulled even tried sanding the inside of the brake lever.
After a bit of a condor moment I tried a light smearing of grease in the hole, first go fitted straight in. The rear brake is now perfect.
My OH has a wee with a wooden feel to the back brake so I thought its worth a try, however, I didn't strip and re grease I sprayed the inside of the pivot with about half a can of WD, I couldn't believe the difference it made.
Worth a try I suppose.