I've noticed a fair bit of vibration on the port main engine and am now looking at the front of that engine where it drives a hydraulic pump (which powers the thrusters + the windlass). On the front of the crankshaft is a Centiflex coupling which drives a Spicer flexible driveshaft (about 10" long) that in turn drives a clutch in front of the hydraulic pump. This Centiflex coupling has one bolt missing, and I believe it's an M20 bolt, so not a small one. In addition to this missing bolt, there's a fair bit of slop in the coupling, even near one of the bolts that's still there. I took a short video of the setup and movement; hopefully this works: https://vimeo.com/495100482 This type of coupling is completely new to me, and I'm trying to determine what's best to do with it. Should I just find a replacement for the missing bolt and tighten everything securely, or do these Centiflex couplings have a limited lifetime and need to be replaced periodically? It's just under 20 years old. What about the Spicer driveshaft -- maybe get it rebuilt with new U-joints?