Thanks for your replies. After another lot of treatment for his bad leg, he's luckily had no other problems in that area and mobility seems normal. Was watching him groom himself last night and again everything seems fine. I'll have a go at brushing him anyway (offering treats might be a good idea as he's always liked touching on his own terms, only on head and shoulders and when he's in the mood. I've also just been out and bought some wet cat food with omega 3 added, so will give him one of the pouches every day.
Have looked up information on thyroid and he isn't showing any other signs which can be linked to this, but the signs are something I will keep an eye on over the next few weeks.
Any other comments/advice are still welcome!