yep it's only the orings....
all the orings that are touching directly the bolt should be changed.
That means the inner orings of the can and the sleeve...and the sail oring on the bolt directly
If you take your complete bolt setup out of the gun and move your bolt foward and backwards you shoudn't feel a drag or very little restrictions.
I would say with what i know changing the orings will solve the problem at 90%. I am keeping the 10% for either a solenoid problem or reg problem