What pressure do i leave my gun at?

The max it will hold is fine. I've left one of my Benjamin Bulldogs at 3000psi for 6 months, with not a care in the world. I dusted it off, cleaned the barrel, and it shot like it was brand new.

Give a drop of pure silicone (I use RSW) in the fill port right before your fill, and you're golden.

I always put away my guns after a shooting session and it's always at 100 BAR,....good enough to have a couple quick shots on tap if needed and when I pick my guns up and they are not at 100 BAR I know something is not right.

There is no correct number but anything up to max is fine for years of storage. You can't hurt anything and if an o-ring ever fails you can replace it yourself for pennies. You can always get the instruction you need here.

When it comes to storage just remember it's always better to store under pressure & not "empty" the reservoir. Don't overthink it as to OPTIMAL storing pressure so all answers above are correct.

The principle behind storing it with at least some pressure is that it keeps O-rings / seals conformed to their mating surfaces. If stored empty, a seal can potentially relax and have a hard time seating once you go to refill, particularly if the material has become harder / less compliant over time. Granted I have not seen much evidence this issue is very common, at least not until the material has degraded so significantly that it would need to be replaced anyway.

Meanwhile the argument against storing at full pressure is that it puts stress on the seals. That can be a real thing if the seals are poor quality or have some other deficiency (e.g. insufficient durometer to prevent extrusion). My take on it is I’d rather find out sooner rather than later so I can go ahead and deal with it…as opposed to taking the risk of topping it off and having a seal fail suddenly at a time when I really want to use the gun.

I keep all of mine at or near full pressure.

I think one reason for not fully emptying a pcp is that hammer spring preload on some guns will hold the valve poppet off it's seat with no pressure so you'd have to hold the cocking lever part way back to close the poppet and fill it again.

I had been in the habit of leaving my guns fully charged so I don't need to start a shooting session with a pump. However, after looking at the condition of the seals in one of my guns after 5 years of service, I have decided to stop doing that. 5 years is pretty good service for o-rings, but I did notice a number of them had some extrusion damage from being under pressure (and sometimes spending several months at full pressure). My take is that it's probably worth storing them at the low end of your fill range and just topping off before you start shooting. I now store my guns at the pressure I stopped shooting.

Can I suggest? empty the plenum for couple days?
Not my idea, I learned this with my L2, the Reg was creeping like crazy.
That will create an opposite pressure on the Reg piston and will help self deform to the other side shape (with Leshy no piston but a ceramic ball agains a ABS puck).
And worked like a charm. Before was creeping 15-20 bars and now only maybe 2-3 bars.

Thouse times I had any leak on my guns, is usually after I have taken it appart, and put it back again. I store my guns usually 200bar+, as then they will always be ready to shoot. I like to fill after I shoot, not before. I am still more worried about a leak after taken it apart for adjsuting a reg, or something else. Maybe the lifspan of seals can be prolonged a couple years by storing it with less pressure, but that is not so fun in my opinion.

Is the Kral NP03 regulated? For a regulated PCP, just below the reg pressure is good becuase it relieves the force on the reg seal, and stops excess force which can deform the seal if the reg would have crept over the storage time. (it can't creep if the main cylinder pressure is below the set point)

The longest trouble free air gun I have is a steyr LP10 air pistol. Think I bought it in 2008 (the cylinders are stamped 2007), and since I did not had a compressor back then, I usually stored it with what pressure was left in my fill bottle, between 200 and 150bar. It is a 200bar max fill gun. One cylinder attached to the gun, and the spare lying in the box. Have never changed any seal on it yet. Think maybe there is a slow leak on one of the cylinders now, but it can go several month between each time I use it. There may be a difference on storing a gun at 250, or 300bar? I really do not know.