The bubbles might be from a leak in the suction line to the charge pump, often at the suction filter, as you have found out. There is also the possibility that another wheel motor hose is slightly open, though the fact it happens in forward and reverse makes me think it is a motor or pump issue. Any oil weeps, or leaks?
How many hours are on this 425?
With the tractor up on blocks, you can listen to each wheel motor. If one sounds loud or problematic, that's probably the one to go after. I use the front bucket to lift the front wheels off the ground and then put blocks back close to the rear wheels. Lowering the FEL a bit raises the back, and lets you get all four wheels up quickly. I use jack stands or 8x8s on mine.
How far are you from Tazewell?
All the best,
Peter