7.5% is still a little high for my liking personally. Pressure inside the GC should be fine if its reading stable (what is your working pressure?), but the needle on the pressure guage is external, as long as it is around 100 PSI going into the GC it should be OK.
I suspect you may have a leak external to the instrument, maybe on the manifold connected to the helium, or even on the copper line going into the GC's EPC. I would check there first as any leak here will put air directly into your helium stream and no matter what you do to the GC, if there is a leak there, it will keep reading high.