You might check the pump by pulling it, remove the reservoir and look at the back side of the pump. There is a snap ring that holds a cover in place. Behind that is the pump (impeller vanes). If that snap ring pops out you’ll still have flow, no leaks but no power assist and it will foam the fluid after a while. Not saying this is your problem but something to check. I chased the same symptoms you describe for weeks and found the above to be my problem.