Sand/Grit In Driveshaft Tube and Crankshaft Coupler

[iheartbooze]

I have a 94 Mercury Tracker 75hp. When I pulled my lower unit, I noticed a lot of sand and crud on the splines on the top of my driveshaft. I cleaned/regreased, but after having trouble reinstalling, when I pulled it back out the splines were covered with sand again. There seems to be mud and sand both in the driveshaft tube and in the coupler where the driveshaft splines meet the crankshaft. Is there any way to run something up the tube and clean/flush that gunk out of there rather than pulling the power head? I've noticed some chunks of old dirt dauber wasp nest under my power head which may be the source of the sediment, but I don't know if it can get from there to the bottom of my crankshaft or if it more likely came from below. The driveshaft was also missing the little rubber sling seal above the water pump, which might be an issue.