Take the shock out, and see if the spring is seated on the seat on the inside of the frame, or if there is a problem with the seat. It could have a damaged upper seat, or a broken weld in that area.
The snap you heard could be the steering stop on the spindle, and lower A frame rubbing, that is unrelated to the squeak. Again harkening back to my days working on the grease rack at the Pontiac dealer. If the wheels were cut to the steering stops (turned fully to lock), and you traverse a driveway approach from the street to the end of the driveway, you many times hear a snap as the 2 stops slide across each other, and it can be quite loud. It sounds as if something broke in the front end. There is a fix to stop that snapping, you just lube the stops with grease.
The steering stop snap won't make any difference in your spring squeak, it may be just a coincidence that you heard that snap, and the squeak reappeared.
Again at this point, you need to make sure the upper end of the spring is seated correctly on the frame. It's very easy to miss the seat when you're putting it back together by yourself. I've done it too.
If you missed the seat, the rubber washer could have been cut by the edge of the spring seat, rendering it useless at this point, and the squeal is back.
If this is the case you want to pull it back apart, and when you re assemble it , stop when you raise the A arm back up, and look up through the shock hole to make certain the spring is fully seated, before you but the castle nut on the ball joint stud.
One other possibility that I can think of. Once, or twice time in the last 50 years of wrenching, I put a set of new shocks on a customers car, and it developed a squeak. The shock dust seal was squeaking, not the spring. I ended up getting another shock from the parts store, and replacing it to stop the squeak. That would answer why it possibly went away when you lubed the upper spring mount, enough WD 40 got on the shock shaft to temporarily stop the squeak. By the time you got the spring out, and back in the lube got dry again.
That is a long shot diagnosis, but I have had that happen once or twice on shocks. The way I traced it was lying under the car I had someone else bounce it, and felt all the parts as they squeaked. I could feel the vibration as the shock wiper seal squeaked. I suggest you trouble shoot it the same way to find the source of the squeak, feeling each part to see if you can isolate what is binding, and squeaking. Yeah sometime finding noises in cars is a real PITA.
Hope something I posted helps you find this noise.