They look really great James - very healthy looking, I'm not sure about the gunk but I would clean with soft wet cloth, I have 4 at the moment the first 2 the black ones (stinky and Little Un) are doing great and zooming around and used to the goat and have learned not to go to near the young kid 'Bandit' or they get chased by the mum, the 2 younger ones - white ones (Coffee and Cream - Coffee has a cough but is still hanging in there, hoping she's going to pull through), they see me and dash up and follow me every where, I guess it's won't be that long till I get bowled over!