I go through a quart of drive fluid in an hour of run time. My bilge is full of drive fluid. When I top it off and let it sit overnight....no leakage. Pulled drive off, bellows is dry, no sign of water or fluid. Any ideas?

I would check the resevoir bottle and the line coming from it to see if you have the leak there or along the hose anywhere.
I had a leak on my Latham hydraulic fluid resevoir at the point where the line entered the resevoir and it did exactly as you are describing.

Make sure the rubber gasket is in the reservoir cap?

What drives?

You running a Bmax, when I had one it would blow the damn oil out of the tank for some strange reason, know way could I keep it even half full, that is most likley the problem see if when it blows out bring a quart of oil with you and go out on the water, I bet the level in your bottle doesn't change once it blows is out...

They are B1 drives. The only way to tighten the nut that goes into the transom assembly is to remove the engine, What a PITA. There is no sign of fluid around the bottle so it looks like an engine will have to come out

I would be inclined to think that the fluid is coming from the drive itself. More then likely from the input shaft in the upper. You can pull the drive and see if the bellows is full of fluid but the best quick diagnostic is to have a service department pressure check it. I would also roll the engine over (not start it) during the test to see if you have a bad spot in the shaft that is causing it.

inside of bellows is dry as a bone

Sandcraft,
Have you tried pressure testing the drive, while on the boat, over night? I would think if it didnt leak without any psi.. then adding that could help you determine where it is coming from. I would add a guage and 5psi to the drive and see what happens.

I think it's simpler than that.
I think you might have air trapped in the drive. Underway, the air expands, and burps fluid out of the reservoir vent.

Rule that out before you start major disassembly.

MC