A Likely Solution? I believe I have found and stopped the leak. At least for now, and seemingly for the most part. I'm posting this in thanks for those who contributed above, and hopefully to help others who may encounter a problem like mine in the future! I was loosing 4" overnight and now, it's maybe 1/4" or less overnight. (Temps here are 40-50 so evap should be at a minimum). I realize I still may have some small leaks. I spoke at length with a guy who plasters new pools professionally, asking about those hairline cracks. He said that since they were above the winterized water level, he suspected that they were due to drying out of the plaster with the water level lowered. He finds that the hairline cracks like mine usually disappear once the water level is raised, due to adding moisture back to the plaster. He said that in 20 years of plastering pools, he had only found one pool materially leaking through this kind of hairline crack. So just to be cautious, I did apply a skim coat of silicone to them before refilling, though they were not my main suspects! I got on a mechanic's creeper and spent several hours examining the tile line around this 40' pool. I found about 8-10 openings in the grout between those tiles at various places from 1/4" up to 2".I cut out the bad grout and replaced it with silicone for a temporary repair. I know that matching grout might have been better - I just didn't have any available on short notice. I also spent a fair amount of time in and around the pool side openings to the skimmers. There was some obvious missing grout there, and I did carefully seal the vertical and horizontal joints between the skimmer box and the plaster. (On my pool, that vertical joint was up inside the skimmer, maybe 4" from the face of the pool wall) I let that cure about 8 hours and filled the pool. So far it's 95% better than before! Now that I can finally keep the water level up to the skimmers, I can finally run the pump . Once we get a clear pool, I will dye test everything around the tile line, the skimmer box, and those pesky hairline cracks, just to make sure. Interestingly, in posting this on this and a few other forums, I don't recall anyone suggesting a look at the tile line. Thankfully, numerous folks did suggest having a look at the interface between the skimmers and the structure. It's a great relief so far, though I know I will have to keep an eye on things, and maybe later cut out the silicone and replace it with grout!

We had our pool installed 22 years ago. The model was called a Hallmark pool -- top 3 feet is fiberglass, and the rest is gunite with a ledge all around. There is a 3 inch wide strip of vinyl that is attached to the pool coping (where tile would be at the water line.) Originally there was another vinyl strip that slid over that. I need to either find the replacement outer strip of vinyl or cut the existing vinyl off of the coping. It is almost 1/4" thick and very hard. Any advice would be appreciated.

I'd go to a reputable pool dealer in your area and ask. To have our pool re-coated with gunite and some minor deck repairs was $13,000 8 years ago. Pool was 20x40.

If a sun shelf is done right, it can easily eat up a ton more gunite than regular pool floor. The shelf should be dug to below the frost line and filled in solid from there up. Otherwise you could easily have water freeze/thaw under the shelf and cause issues. 1. I am installing a heat pump on mine... but I have no real-world experience yet on this. Gas/propane will heat faster and earlier/later in the season. But will cost more. 2. I would just recommend that you insist that it is all on the engineering drawings and not just "off-the-cuff" by the PB. That way an engineer signs off on the whole thing. I'd really recommend the LED light. Add a second one if you want to be sure to get full coverage. An LED light draws about 30 watts... as opposed to a regular light that is hundreds of watts. I had 3 LED lights installed. Will not have them on for a while yet, but I would not go with anything other than 12V LED pool light.