When I had to clean my reservoir filter due to a whining noise the fluid wasn't changed in around 10+ years so it was overdue. Cleaned the mesh filter but re-used the o-ring and it bit me in the ass. Kept whining despite the many times bleeding it with the wheels up so I figured something was wrong with the pump. Decided to rebuild the pump with new seals (didn't need to do this) and the kit came with an o-ring for the reservoir. Bleeding session #3 using Toyota instructions and it was finally quiet. Pinched o-ring was my issue so I highly recommend replacing it if you remove the reservoir.

I used Tim's video for the PSF flush - worked great! Brand new fluid is great in the system. You don't have to run the truck to flush it out, you can just lift it up on jack stands and turn the wheel lock to lock to manually pump the fluid out.