Slave cylinder runs compketely out of brake fluid. Is there a small leak? I refilled it about a month ago. And its out again should the lines be bled before? Or has it developed a hole somewhere? (I bought the truck a few months ago).

 

You need to find the leak?

You should be able to see where it is leaking .

If the slave cylinder is empty since this is the lowest point that is where the leak is.

If the leak is in the Master Cylinder the fluid stays in the lines below the leak.

when one fails it is best to replace both and the rubber hose.