Pour some Marvel Mystery oil in the case, turn the crank over several times, and let the Marvel Oil sit in the case overnight. Drain it out the next day. That should clean all the sludge out of it.
If there's a lot of sludge in there, there's a good chance that water got in the case and your crank bearings could be rusty. The crank should turn very quietly and smoothly. If not, it may need new bearings.