Isn't the spec like 140-160 psi or something like that :\
Exactly, I think the lower acceptable rate is around 140+.
Start saving for a leak down test (over a compression test) that will tell you where you are losing compression. It could be rings, intake valves, exhaust valves or even head gasket. Rings usually mean overbore with new pistons and rings, ca-ching, and while doing that, better re-seat the valves as you reseal it with a new gasket kit.
And do you really want to be known for trading in a dead horse, so-to-speak.:shrug::shake: