You are Fumblin' no more!
Don't waste any more time--get some help with the brakes. A tree or a fence post at 5 miles and hour will do damage to body parts. I know you think, "It cain't happen the way I'm drivin' 'er," but it can.
Those little holes in the cap really do have a purpose and allow for the balancing act because the brake system is NOT a closed hydraulic system. I would clean up the original cap, get a new gasket for it and use it.
As far as the overtightening part, "snug" is good enough.
I love to read about your experiences and progress.
