Richard, brakes are Important Stuff, and you just confessed to happily leaving the cap off the brake fluid for a long time. Brake fluid and moisture are mortal enemies. That may not be your actual problem, but....
I have it on good authority that you are very good at the things you are good at. Bus repair happens to be not one of those. Please let a mechanic repair your brakes for you.
"A man's got to know his limitations."
- Clint Eastwood as Dirty Harry.
All my best!