I removed a dead SUNLITE and bought a new Pentair Aqualite which was supposed to fit the small niche. Well it "almost" fits in. I had to cut the clamp bolt shorter on the backside. Now I can get it mostly in, but the niche has a "flat" at the top and bottom that are keeping the light from fully seating. I was thinking if I could somehow remove the lower flat, I could get the light in further. I'd hate to trash a $185 light and spend another $215 on a SUNLITE. I can post a pic later today.
Part #4 is what my ring looks like.
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Here's what the old light looks like: