Having had good experience of Driffield ...as I normally race there once a year with the British Cross Country Championship... the place is always wet and has the properties of fine grinding paste.Least I would do is change the diff oils, and grease the propshafts....and serious consider checking the wheel bearings / regreasing and giving the brake calipier pistons a good wash .
A garden sprayer....as in pump up type are a handy tool to have if your doing offroad courses in deep mud....you can normally wash out enough mud to get you home.
[I have used 'water bottles' and pierced the cap with a knife to use as a small jet washer in the past]