Sorry, very tired and I should have posted more info.
This thing is connected to the drive shaft and the trans. I was told it compensates for vibration or small out of alignment issues.
I'm guessing it was a lack of grease that did it in, I didn't know it needed maintenance
. We're starting to shake down the boat for the haha and cruising, and it started with some nasty grinding noises and ended with the tranny turning it, but it didn't turn the shaft.
I'm trying to find out what exactly it is, who makes it, how to repair it, or have it repaired or replaced. There's no marking on it.
Here's another picture... not sure why I've got tranny fluid leaking...