I was actually referring not to the disc surface but the vent hole in it. I generally use wurth products including the one lozzy pictured (sorry very little mr sheen) but since my post I bought dedicated brake cleaner. I think it is a lot more agressive that the dual purpose wurth and can be used as a degreaser/ solvant (so not to be used on the chain!). Once I have used it, I will feed back my thoughts on it.
Only inside the holes. A delicate operation but one cannot be seen with dirty holes! As an experienced hole man yourself, I'm sure you'll agree.