FX Wildcat Mk III - Leaking Air

Hey all,

I filled my FX Wildcat Mk III up to 210 bar, and put it back in it's gun case for about 3 weeks. Upon taking it out the other day, I noticed that the fill tube had dropped to around 50 bar. So it's still holding air...and it must be a slow leak coming from somewhere. I'm comfortable disassembling the gun to find the issue, I just don't know what to look for. I've had the gun for about 2 years, and haven't done any service/maintenance to it other than cleaning the barrel. Should I lubricate the O-rings? What else should I look for and/or do, to diagnose the leak and put a little maintenance into the gun at the same time?

Thanks in advance!