If there are no external leaks, there can only be two places that I can think of where the coolant is going. As you noted, one is past the water pump seal and into the transmission case area. Pull the drain plug and you will find out quickly if this is where the coolant has gone.
The second potential area is that you may have a faulty head gasket and the coolant is getting sucked into the cylinder. You ruled this out as you do not have bubbles in the coolant when the engine is running.
Actually, there may be a third possibility.... You may have a bad radiator cap. If the cap is bad, you may get some blow-off and lose the coolant through your overflow tube. Look at the tube and see if there are traces of coolant inside.
I would say that you probably have "coffee w/cream" colored oil......
Let us know what you find when you drain the oil.
Al
