er.. WELCOME! I guess!
Not sure about the SLS system - my D2 was on coils before I bought it. Have you got access to a diagnostic (Nanocom, Hawkeye, Lynx, Testbook) which may help. Can you not just disconnect the air hose to that bag and then let it down? CAUTION - I don't know if they have a valve to let you do that.... don't want it going bang on you if you pull the pipe off.