I don't have help for your question, but the picture you posted where the old light fixture was removed shows something that drives me crazy in my 27K Windsport...
Notice where the rounded corners of the old light fixture left the vinyl ceiling with a crease, where they vinyl is sagging below whatever it was glued to? I see this on my ceiling next to anything screwed into it, like the A/C vents, skylight, and light fixtures for example. It's not a new symptom; been like this from the first day.
I have thought about injecting some glue into these areas with a needle but seems like I'd have to apply pressure to hold the vinyl tight against the ceiling while it's drying. A lot of work, and not sure if it would work anyway.
Sorry to go slightly off-topic.
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