After several years of gigging with the F1 812, the corner grille got damaged care of a nasty tumble. Given that I've never found information on replacing this grille anywhere, I've decided to share my successful replacement experience.
1) Getting the part(s): I called Bose technical support and spoke with a nice lady who quickly identified the required grille for my F1 812. The cost with shipping and tax was around $55. Both left and right grilles are identical. It arrived in less than a week.
2) Removing the defective grille: Lay the speaker on its back. I used an automotive nylon pry tool to get under the outside long edge of the defective grille, and bent the grille away from the speaker, releasing the four tabs. Be careful when prying to get under the grille, and NOT the long rubber gasket. Once the tabs are free, you can pull the grille straight up, a little bit at a time. It's a tight fit. Take your time. Also wear gloves. There's some sharp edges. You will further damage the defective grille during this process. The photo below shows the grille removed, the speaker's four tab locations and the long rubber gasket:
3) Preparing the speaker: There are two rubber bumpers on the speaker that facilitate a "force fit" of the grille. One of mine came off during grille removal and I had to super-glue it back in place. The below pics show the correct location of the two bumpers:
4) Preparing the replacement grille: My new grille included two rubber strips that came off during shipment. I super-glued them back in place. Their proper position is shown below:
5) Installing the new grille: With the speaker on its back, position the replacement grille directly over the top of the speaker, and start working it straight down into position. Gently push it in place, a little bit at a time, one side at a time, until it is fully seated, and the tabs snap into their slots. Take your time and don't hammer anything. It's a tight fit.
This worked great for me, and I hope it helps the community.