Long term storage in unpressurized keg

Typically when I keg a beer I will hit it with 30psi to seat the lid and then let the keg sit at room temp for a couple months before throwing it in my fridge and carbing it. I've noticed with some of my kegs that when I go to move it in the fridge and pull the off-gas ring on top to check pressure that little or no gas is released, so I assume that the keg is slowly leaking from the gas in poppet (or the room temp beer absorbed some of the c02?). I haven't noticed any issues with my beer sitting for a couple months, but could this be an issue if I were to store say a barleywine for extended aging? Is the layer of c02 on top enough to protect it from oxygen? Or am I just overreacting to the beer absorbing what little gas I throw in to the small headspace of a full keg? Thanks!

Yes, a bad seal can accelerate staling or allow for an infection to take hold. Why not just pinpoint the leak and fix it? Try spraying your poppets and lid with star-san solution and look for bubbles. It's likely a bad lid o-ring or a bad/dirty poppet. Easy/cheap fix either way...

Not a bad idea to check for leaks, but the CO2 will go into solution at room temps, it just takes a while. Think of it like this, you hit it with 30 psi and leave it. When you bottle it's not 30 psi coming out when you crack the top is it? And you bottle condition at room temps, or slightly above anyway.

Either fully carbonate it before storing or get one of the Williams brewing extra thick o rings, they will seal a keg even with no pressure. It seems like only half my kegs will seal with no pressure.

Even without a leak the CO2 will disappear into the beer. I just check mine periodically (hit the relief valve) and hit them with another 30 psi when they get low.