After a mud race I break the entire car down to the diffs and lather everything with simple green and then pressure wash with a puenmatic engine cleaner gun. The mud just falls out no matter how caked on. I then use a RPM bearing cleaner and spray WD-40 on the kingpin and diff bearings to get any remaining grit out. As a anal retentive measure against moisture build up, after cleaning I run the buggy for a few high speed laps on pavement to burn any remaining moisture in the bearings and it circulates the WD-40.
Every third race I break down the diffs and shocks and check the gears and replace the fluids.