Need experienced N2O help...

[Hammer]

Someone please tell me whether the following is normal, not normal, OK to leave as is, or something that needs to be fixed...

At the ene of my track\street activities for the day, I usually turn off my bottle and purge the line of pressure. A few nights ago, I was so tired, I closed the bottle, but didn't purge....

Imagine my surprise in the morning when there was NO pressure left in the line. It all went SOMEWHERE...

Being that the bottle was closed, the only place I could see it escaping is somewhere in the line or through the solenoid. I've had views from both sides:
Some say that a little line loss is normal overnight if not bled beforehand, while some say it is something that needs to be fixed, as the line/solenoid should keep some pressure if not relieved (even through temp variations overnight).

I am averaging about 120 psi per hour loss while the bottle is closed from the line.

While this doesn't appear to be affecting my performance, I didn't pay good money to lose N2O/pressure that I'm not using...

Any insight on this?

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1998 Mustang GT
14.18@100.56
"Traction Impaired" or "Nitto Needy"