I have a 2002 S80 T6 and was experiencing the same problem. No leaks at upper or lower hoses, floorboard dry as a bone, no leaks from any part of the expansion tank or hoses. I removed the bottom engine cover and could see a little bit of coolant coming from below the timing belt cover, which also covers the water pump. I am about 60,0000K into the existing timing belt (172K on the car), so I thought I'd go ahead and replace timing belt as well as water pump. In removing the lower timing belt cover, the fella who was helping me broke a small plastic T coming off of the thermostat housing which then sticks out through a hole in the lower timing belt cover. I ordered a new one, which promptly arrived in a couple of days. In order to install the T, you have to take the entire thermostat housing off, and it's no small task reinstalling the housing because you have to thread a wire into a slot between it and the block while managing the housing and gasket at the same time. Anyway, I got all the new parts installed, everything back together and started to fill with new coolant only to see it leak significantly onto the garage floor (wanta see a grown man cry?). I pulled all the turbo piping back off, pulled the upper and lower timing covers, and slowly started putting new coolant in once again. This time I could clearly see that the leak was coming from a small expansion tank bleed valve which slips over the new plastic T I described. The bleeder valve comes assembled as part of an expansion tank bleeder hose (Volvo Part #30680933), which I've ordered a new one. I looked all over the forums and could not see any posts which describe a leak at this point. In fact, I feel like this was the source of the leak all along and knowing what I know now, I'd pull the upper and lower timing belt covers off and observe everything with pressure on the system should I do it all over again. Point of all this is that if you can't otherwise find the source of a lead and your thermostat housing and/or water pump are underneath the timing belt cover and you might want to pull the timing belt covers off and closely observe for leaks.