Rob a bank?
Does it cycle with paint? If not, probably the hammer o-ring. Degas and remove the air, then remove the pin (carefully- it holds the internals in against a big spring) and ease out the rear plug below the bolt channel. Then use the bolt pin to slide the bolt and hammer back together and out of the body. Take a look at the hammer o-ring, and if it looks chipped or worn it will need replacing.
I think
the JT's are spyder compatible so try and find a spyder parts kit online or call a store or two and ask around. Just Paintball have a lot of JT Excellerators
D ) and will probably be able to help you out.