Measure the resistance of your existing group solenoid coil and post the results. Ask LM what the value should be.

If you had measured something like 200-250 ml/minute I would think the clogged gicleur theory but at 45 ml/min that makes me think the solenoid or the valve itself.

I replaced the gigleur and the flow rate is great. I have not had that much flow before. I'm now getting 500 ml per minute.

With the repair a new problem has arisen: I now have every 15 seconds or so a small discharge from the three way valve that enters the drip tray to the left of the group head. I have tried back flushing, full power up and down and reseated and tightened the solenoid and the overflow copper pipe.

Upon rewatching Chris Nachtrieb's video I do not recall seeing a black flat o ring between the solenoid and the copper pipe that goes into the group head but there is a round one that sits on the solenoid behind the threading.

The fluctuating discharge is odd and will only stop when I cut the water feeding line to the machine.could it be the mystery o ring that I can't seem to find? I took the sides of the machine off but I don't see it dropped anywhere.

I replaced the gicleur and the flow rate is great.

And I'm soaking my old gicleur in vinegar for a few hours or so?
Tightening all these fittings will not fix an internal leak. You either have a SLIGHTLY leaking solenoid valve or your OPV is not properly adjusted. Instructions for adjusting the OPV are detailed in the manual.

Certainly the copper tubing which attaches to the valve needs to be tight . . . but not much more than hand tight . . maybe a 1/6 turn past hand tight.

This schematic illustrates the MP version (I realize you do not have this) but the o-ring situation is correct. Oftentimes a square o-ring is placed between the solenoid coil and the valve to isolate coil vibrations and properly locate the coil with respect to the valve body. This is not indicated in any illustrations I have seen.