@Legenderyi I managed to remove the oring from my flow limiter (which I'm not using) without too much trouble. I used a very pointy plastic pick, and was very careful not to poke the oring. So definitely possible.
If you don't have the flow limiter to steal an oring from, I measured mine with digital calipers, and then cross-referenced against a metric oring chart, it appears to be a 1.1x3 (ID=3.0mm, CS=1.1mm, OD=5.2mm)
Edit: Didn't refresh to see
@Open Ocean Diver 's response. Looks like my measurements were a touch off.
Garmin Support Centre is where you will find answers to frequently asked questions and resources to help with all of your Garmin products.
support.garmin.com