Brian. I have to go back to an earlier posting of mine. After spending 35 years designing and building transmissions, there is "no such thing as indestructable gearbox" they will always let you down when you least expect it.
Here's an interesting theory. We have all been using rib's for a long time and have come to live with the exceptional sea keeping.
When was the last time you went out in a fast hard boat?
Last year I was invited to sea trial a new engine set up in a well known make of powerboat.40 foot, lots of HP and supposingly very quick.
It was not a particularly nice day but not that bad that you would stay at home. As came out of the harbour with the loud sticks open she shot up to 55 knots which was very impressive, but as we headed West along the Solent it got very interesting and the proud owner soon had her back to 20 knots because the boat couldn't take it.
(as a side line, the only time I have broken any bones in a boat was in a Class 1 which landed so hard I put my elbow through two ribs).
Now then on to my theory. Because the type of boat we use is very safe and handles bad weather better than a hard boat we tend to use them more than say, the average Sunseeker owner who would rather stay in the marina than have the crap beat out of them. The Sunseeker owner rarely has drive unit problems and the rib owner lives on a knive edge everytime they go out expecting the outdrive to go bang.
Why is this? because we expect to much from the units that are available and untill someone comes up with a hardening process or design that doesn't break it is something we are going to have to live with.
My recommendation is to keep the outdrive oil clean and the prop in the water. For referenace Still Never Enough had over 1200 hours on her Yamaha out drive, this was after the North Atlantic trip and a full throttle blast from Tower Bridge to Monaco (99hours 12 min 15 sec) Spirit travelled over 20,000 miles on her origanal outdrive before being changed to go around the world. It is the luck of the draw