My Challenger 2021 has developed a very slow leak. I did add one small drop of silicone oil to end of Foster fitting at last fill - still a slow leak. I suspect it may be at pressure gauge as I have tightened it, but it seems like I could keep right on turning it. Do the stems on the pressure gauge bottom out, or are they a pass-through into air cylinder? Any advice on re-doing thread sealant? Thanks for any assistance.