Gas the marker up take the bolt out look into the breach you will see a long cutout where the bolt pin connects to the ram shaft and infront of that another hole which is where the air is passed though to the bolt. If you can slide your finger into the breach to cover the smaller hole and listen for the leak with the hole covered. If the leak has gone then you have a valve leak. Be very carful when listening for the leak that you dont shoot yourself in the ear it hurts a lot
. If you have found a valve leak you will have to remove the inline reg then unscrew the frame and remove, unscrew the 1/8 bolt that holds the lpr in place and remvoe the lpr then remove the valve and spring from the bottom tube at this point you can check the valve face to see of there is any scratchs on the valve face even the smallest of marks will cause a leak. If the valve looks ok then remove the 1/8 valve plug from the bottom of the body and push out the valve guide (easyist way to do this is push the guide from behind from the top of the body though the cutout that the bolt pin slides though use an allen key)then check the face of the valve guide again if there is any marks on the face this will need replacing. Its also worth checking that there is no debis under the 0 rings on the valve guide. All the parts mentioned above are available from Planet so may not need to send in your marker as i will help you with any questions tou have in solving your problem.
Steve