McMac - Thanks for weighing in on this, especially with experience from the Northwest and multiple vehicles.
Terry - Very good point.
First off, my apologies for the VERY late reply to both of your messages!
I'm calling this one solved.
Here's what ended up being the fix for me...
1) On an unseasonably warm, sunny day, I left the sunshade closed and opened the back of the sunroof upwards ('vent' setting).
2) Through the partially open sunroof, I sprayed the top of the sunshade area as thoroughly as possible with a fairly liberal amount of unscented Febreze (
https://www.febreze.com/en-us/products/ ... -freshener). I couldn't reach everywhere I would've liked to, since I was using it straight from the original spray bottle. I was going to rig something up for better access if this showed promise, but there was no need.
3) I closed the sunroof and let the PF sit in the sun.
4) I waited a few days and opened the sunroof shade from the inside with the sunroof closed. No smell at all.
This is a very simple solution, but it worked for me and so far no re-occurrence and no need to redo.
Thanks to all who contributed!