Right now the handle cannot be compressed. It seems like it's all gummed up. That's the extent of the diagnosis I was able to come up with.
At this point in time with what i know it is not certain a cylinder rebuild is needed.
Not even any new parts
Thinking out loud I would suspect new caliper pistons and stuff. They can rust.
But the solid handle can be locked in pressure only .
That goes away when the system is opened.
I Have never heard of gummed up brakes .But i have heard of water coming in that's why
brake fluid replacement is recommended.
I did not do that for many years + 10 and ended up paying the price for it
The brake pistons rusted and stopped working. Seized
If this was me I most likely would go for the procedures used when changing the fluid.
Se what happens
And if that not works open a hose connector closer to the handle so the handle has the possibility to move if there is locked in pressure.
I would also consider Machines offer in
# 276
Above i think it looks fine enough.