What is the cause of a bravo upper gear failureon low hour drives? How does one avoid bravo failure?

Easy out of the hole if you have big power, watch your throttle if you catch air, the re-entries are very hard on the drive. Depending on your horsepower, no matter how careful you are eventually it'll die. If you have a small block, or big block that's non mag or non ho it may last forever for you. 500 hp or better, it's just a matter when not if.

A year or two ago, Mercury had a bad run of upper XR gears that would fail at 25 - 50 hours. There were a couple of threads on it. Other than that, just what was said. I run billet top caps with integrated water cooling and they add strength on the left hand turning drives.