Brakes

If your system will not bleed, try this.
Open both your rear bleed valves.
With a shop vac, suck out the fluid from the resovoir.
If your front wheels are the same, no bleeding, do the same.
When empty use a bycycle pump with an inflating needle on end. Close all valves except one. Start at one corner (rear) and have someone pump air down.
No air? Blocked line. Do not use high pressure air!
If you get good air to all 4 corners fill resovoir with new fluid. Rear first, leave the right rear valve open. Pour fluid in until it starts to bleed. Close valve & open left rear, Got fluid? Close it & finish topping up front lines. Install master cylinder cap/caps and proceed to rebleed your brakes. Top up fluid and away you go slowly to test.
There are a few soft parts inside the master cylinder.

You really should check with a local brake shop and explain the situation, ask for advise.