Get a dowel appropriately sized for the bottom hole in the saildrive
intake (3/8"?) and long enough to reach through it and stick it up into the drive. Move it around a bit and in and out and it will break up the barnacles
that grow up there. One of those plastic rods that are used in venetian blinds to close them when you twist it works perfectly.
Then, next time the boat is out of the water, add proper intake through hulls and a strainer and plug
off the saildrive
intake for good. Trust me, your life will be much easier after that.