what is the max air pressure for the struts in the air suspension

You must have aftermarket struts installed. What brand are they?

These are the original parts

Are you kidding? The OE system is self-calibrating, but is infamous for crapping out after only a few years for myriad reasons. Mostly it was because the "bellows" cracked and leaked after only a few winters, resulting in the "kneeling down" Subie each morning. The $400+labor struts were a horror show to deal with, because after you replaced them ALL the damned pump would screw up! Dealers made quite a pretty penny charging ultra-frustrated LS owners $1800 to swap BACK to simple non-adjustable shocks procured from salvage yards! I'm shocked (npi) that you have an old LS that still has these balloons. Their rubber bellows were no better than CV boot rubber, and have no hope of holding high pressure after a few years.... An easy test is to let the pump air them up, then run around and mist the bellows with soapy water and watch them blow bubbles through the micro-cracks! Sorry...but I recommend you give up sooner than later.