While motoring along about 3200 rpm on my alpha one / 5.7L Merc, I
suddenly heard a metalic clanging. I shut the engine down, checked
everything, and attempted to restart. The engine wouldn't turn over.

Once back at the marina, my mechanic pulled the boat and the lower
unit. Engine was fine, but when they put the lower unit on the bench
and tore it down, the upper gearcase was hosed. The gearings looked
like someone took a sledgehammer to them, and the case was pretty
chewed up inside, as well.

Mechanic states the lube was fine when they opened up the unit and
cannot give any reason why it imploded. The drive is (we believe) 16
years old and orginal to the boat. He had a used (upper) gearcase in
stock and based on his recommendations, I had decided to go with that
(He did offer to either rebuild the old one, or order a commercially
rebuilt one, as well). We're back on the water, but I have a few
questions for those of you who know a lot more than me:

1. There was no mention of the lower gearcase. Was it okay to bolt
the used upper on without at least tearing down the lower to insure
there was no debris there? Should I insist this be done now, after
the fact? We have about 3 hours on the replacement. The mechanic
states there is a magnet in the lower that would catch any debris.

2. I now have a "hydro" or "harmonic" sound coming from the lower
unit when underway. The mechanic states this is the gears actively
meshing, and is normal, being loudest in new I/O's. Is this true?

3. Ealier this year, I had a loose lube plug, and the lower unit did
experience some water intrusion into the lube. This was immediately
corrected and we have put about 20 hours of use on the drive since
then. Would this cause the upper gears to self-destruct 20 hours
later? Could I expect the same at some point in the future for the
lower gearcase?

Any other information or advise you can offer would be greatly
appreciated.

Regards,

Coff