Specific to your question, when you "filled the cylinder with fluid". Was that just to top it off..... or was it concerningly low or empty? You should start with a bench bleed if it was concerningly low or empty. You might try plugging the out port of the m/c to see if the pedal is "on top and firm". If so, then the m/c is good and the problem is elsewhere in the system.
Now, looking forward, If you find it needs $$$parts to repair, it would be beneficial to determine "What" your project plans are.
Good luck
