Thanks all for sharing, I discovered I had a gradually worsening ACS leak down, today I pulled the trunk off my '13 Spyder and tada, leaking Check valve, (BRP part number 706000831). Cleaned it, leak checked it off the bike, no leakdown, replaced it on the bike and repressurized the system and am now impatiently waiting to see if it holds pressure, it's already held better than last week...
Check Valve 706000831 connects to the ACS compressor pump outlet and looks like this off the bike,