Andrew,
Hopefully after a mid-year maintenance check to work out the bugs, and an annual / 150 check, you will be back up and running with fewer issues.
I had a similar story, although not as many issues, but certainly had a few. Less than I expected actually.
Our airplanes are like twin brothers--both were owned at the same time by the same guy--Brian H.
Both our planes sat together in the same shop awaiting some work.
Both planes have G600/GTN's and low time dash tens.
Both planes had sat for a while and needed a some love to bring them back to life.
No Idea why a guy would own 4 airplanes--(2 690B's !!) at the same time and neglect most of them, but who knows.
Interesting story, first day I got home, the FBO comes out and says, "hey did you buy that plane from Brian H, I see the ownership on flightaware" and I said yes, why. He says,"He bought a Cessna 421 out here not long ago and it was in our shop for several weeks".
That Cessna 421 is now for sale.
So our airplanes are forever linked by the common ownership history.
PS: I Turn off Oxygen on the scott cabin controller every flight. Its part of my flow.
I never touch the tank in the back though.
Yours has/had the EROS masks, and as I understand it, they are temperature sensitive and can tend to leak on the ground. Citation pilots complain about it all the time. I have an oxygen filler tank kit now, so no longer worried about the levels. The original masks aren't really any better or worse leak-wise, from what I can tell.