Dave the lathe sounds fine, the spindle seems tight and smooth. I re-adjusted the spindle bearing pre-load and I think the spindle bearings are fine, keep in mind they are upgraded NSK bearings. It spun really free and smooth as I approached zero end play, the final 1/16 turn of pre-load after eliminating the end play did exactly what I expected, my dial indicator showed zero movement and I could feel the pre-load in the spindle then. I guess I would describe it as slightly more difficult to turn the spindle but still very smooth and free. I had snugged up the pre-load even further before, this had no effect on the spiral pattern at all.
The only thing that has changed the spiral pattern has been the amount of belt tension. On the G4003G there is a separate drive shaft the motor connects to via the belts, e.g. the belts don't connect directly to the spindle, they spin this drive shaft which in turns spins the spindle via gears in the head stock.
So too little belt tension and I get the spiral pattern. Too much belt tension and I get a different spiral pattern and a bearing doesn't sound very happy. With just the right amount of belt tension the spiral pattern mostly goes away. Its not the belts, I have tried both the link belts I had on the lathe and the Made in USA variable cogged NAPA rubber V belts. I tried both 2 belts and single belts of both types just to eliminate any harmonics that two belts might be producing at a resonance. None of this had effect on the spiral pattern.
Now that my annoyance meter as dropped from 10 to 9.7 I will troubleshoot this a bit more this evening.