Drive couplings are designed to wear out, rather than take out more expensive items. It isn't a matter of if they will fail, it is when. Some go after a season or two, others last for several years. Annual greasing is a must and should be done when the lower unit is pulled. Good time to replace the water pump impeller.
High horsepower/heavy boats will see more wear than lower powered/ lighter boats. It is essential that engine alignment be checked and adjusted if needed on a regular basis, or any time there is a lower unit strike. That prop with a blade missing probably isn't the only damage that occurred. The engine may have been knocked out of alignment. Greasing is must. Unfortunately, the drive has to be pulled off to do that.
The high cost of repair is due in part to the fact engine removal is needed to change the coupling. Good time to replace the bilge pump, if yours is buried under the oil pan.
I had a coupling fail after 3 seasons on the lake. Sea Ray Sundancer with the 454. Heavy boat, lots of grunt. The actual coupling failure happened at idle speed heading out of the marina. All of a sudden, without any noise or warning, the boat slowed to a stop.
A visit to one of the more active marine service shops allowed me to see stacks of worn couplings in the corner of the service bay. Routine repair for some.
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