You had so
much dirt in your filter I strongly suggest removing all the tubes and make sure they are clean.
I drained the headstock yesterday. The extension tube unscrewed from the casting rather than the drain plug, which made quite the mess. I was able to route most of the oil into the drain pan, but more than I liked ran down the casting, sheaves, and motor. Fortunately I had PIG pads to sopp up the oil. I mopped up the remaining oil and what grunge I could in the bottom of the case with paper towels.
I flushed the headstock with mineral spirits (less viscous than kerosene), paying special attention to flooding the bearings. I mopped up the grunge in the bottom of the casting with more paper towels. The mineral spirits reacted with something in the remaining oil and created small flecks of whitish slippery stuff like paraffin. Thinking it was good to get rid of that stuff, I wiped out as much as I could then flushed the area with denatured alcohol, again flooding the bearings and rotating things by hand, followed by wiping everything down with paper towels.
I've pulled the tubes and blew compressed air through them. The flow seems good. I confirmed that the air also spins the oil flow indicator as long as I put my thumb on the open manifold fitting.
I decided not to pull the sight glass, but did reach into the case and clean the glass with a Q-tip.
I refilled the case with ISO46 oil, making sure to splash oil into the bearings while rotating the input shaft slowly.
I ended up adding about a liter too much oil, so am now waiting for a big syringe and beaker to remove the excess.
When I rotate the input shaft a few rotations I am getting oil into the flow indicator, so the pump is working. I'd like to see a little more flow even when I rotate the shaft by hand, but maybe the input shaft needs to be spinning at 50 RPM or more to get noticeable flow?
Also, it's clear the pump only pumps when the spindle is turning since the pump is mechanical and driven off the input shaft. The manual makes a big deal about making sure the motor is wired such that the motor rotates correctly so the oil pump works. How is oil pumped when the gearbox reverses spindle direction?