Small bolt leaks are usually caused by the Rear breech oring(14) or inner bolt valve oring(18). Clean the bolt and body of any debris and replace that orings. Lubricate with Dow 33 or similar lubricant.
If still leaking replace the rear shaft oring(22) and the out bolt valve oring(12) and check for any damage or scratching around the bolt tip(15), bolt shaft(25), bolt valve(21), and body(1)
If the bolt is shooting forward and a large leak is coming from the bolt check if the rear breech oring(14) is missing. If the engine is ever removed while still pressurized it will cause the rear breech oring to eject down the barrel. This video shows what to check and the trick to replacing the RBO: https://www.youtube.com/watch?v=VtNkSxMj0vI
If the marker is still not operating correctly contact Valken customer support. Please open a ticket with our customer service department. To open a ticket, please click on the chat button on the bottom of this website and our customer service representative will be happy to assist you.