2nd that, their videos are excellent. With an I2, my money would be on the lowering or check valve seats. These valves are super easy to pull apart and inspect but not much you can do if the seat is damaged. Then even if there isn’t anything visible, something may not be machined true. In some really old I2 manuals they talk about lapping these seats by hand on site but I’ve never gone that far. We typically just replace the valve if one of the piston seats are suspected.
