Venting, these engines are a nightmare!

I have twin 100hp 4-stroke Yamahas. They have about 900 hours on them. So
far this season I have developed major problems with both. I'm begininng to
question the longevity of the 4-stroke yamaha. I'd guess that there are not
too many of these engines with 900 hours on them. I'd be willing to wager
that these engines are flawed. I think it is the same block as the 90hp so
the problems might also be on these motors.

The problems a

1) the oil pump has about a 900 hour lifespan before it begins to leak down
the driveshaft and make a mess of everything. This has now happened on BOTH
my engines. Seems more then a coincidence.

2) one of the engines leaks water and exhuast into the engine oil. This one
I am still diagnosing but I think it is the plate(gasket0 between the
powerhead and the upper unit.

For both these problems the powerhead needs to come off. The only saving
grace is that the powerhead is fairly easily removed and reinstalled.

Anybody else having these problems? Anybody else have either 90, 100, or
115hp Yamahas? If so how many hours? I'd keep a close watch on these
issues if you are getting up there in hours.