This is a follow-up to my previous question: How can I fix a hairline crack in a thin wood panel of an exterior door?
While getting ready to apply wood glue (actually a mixture of wood glue and sawdust/sander dust) to the "hairline" crack in the door, I started scraping away spackling compound from my previous repair so the glue could find wood to stick to.
But after scraping for a while I realized that my spackling repair was not the only one. The house's previous owner had apparently spackled and painted over a huge crack in the door. After removing all the spackling, the crack turned out to be 1/8" wide all the way through the 3/8" thick panel. The crack runs for 12" top to bottom. The crack is oddly consistent in width throughout, except for a small part at the top where a thin chunk of wood is still in place on the inside.
Here's a picture. I put blue tape temporarily over the outside crack to prevent water damage and chilly winds while I figure out how to fix this.
Should I try to stuff a 1/8"x3/8" shim into the crack and glue it in place? If yes, what glue to use for a high-vibration, non-clampable, and exposed-to-direct-sun (under black paint) area like an exterior door panel?
If a shim is not advisable, what are other good options to fill such a large crack?