81 Custom Brake Problems

[M2CI]

Hello all!  I am new here to the forum but was doing some work and ran into some problems.  I am a novice mechanic, but please do not hold that against me.  

I have an 81 CB750 Custom that I have had for several years now.  I have not been able to ride at all this season due to my nephew being diagnosed with cancer earlier this year (he is already in full remission)!  Since I work for myself and am not married, I have been in Phoenix helping them out with the hospital stays and doctors visits.  My 750 has been outside under a motorcycle cover.  I started it about 3 months ago, at the beginning of the season but did not ride it and am now working on getting it in great running order since it has been sitting since last season.  I sat on it to pull into the garage and the front brakes were sticking to the point that I could barley move it.  I got it in the garage, suspended the front wheel and it would not turn freely.  The front brake lever was not responsive at all.  I checked the fluid and it had some in there.  I went ahead and topped it off and the brake lever was more responsive.  I removed the left caliper (it has dual disk brakes), pushed the brake lever, the brakes closed, but did not release.  The brake pads are now together (lke i said, I am a novice).  I read some forums and read that the heat can cause expansion, thus causing the sticking problem.  I read to unscrew the capped valve and it should release some fluid and could release the piston so the brakes would release.  I went to do this and as soon as I put pressure on it the valve snapped leaving the threads behind (I figure I will have to drill that out). No fluid came out, but I figured it's because it is still plugged at the bottom (not 100% on that). But now I am not sure what to do.  Should I completely disassemble the caliper, or is there something else I should do?  If so, is there anything in particular I need to look out for?  I am including some pictures (well it is not letting from my iPad, so I will post and immediately put some pictures from computer up if I cam figure it out).  Thanks for any advice in advance.

[M2CI]

Alright, that did not work.  Let me try again.

r

[TOOLS1]

Loosen the break line fitting just a little. If fluid squirts out, then the problem is the master cylinder. If it does not, then the problem is the caliper. Either way you should probable rebuild them. They are 30 years old.
TOOLS

[M2CI]

I will try that 1st thing in the morning.  Is the rebuild simple for the calipers?  What about the master cylinder?  Thanks Tools, I really appreciate it.