Grooming a month back I noticed a couple of small scabby, waxy type lumps which are around the very outside of the back of where the saddle pad sits. It doesn't seem to be an area where the saddle is in contact with and so I ruled out tack at the time. My RI had a look and said they were nothing to worry about but when I pick at them he wanders about until I have removed the head. I can brush it with curry comb no bother and he is fine under saddle but they seem to keep coming back. What could they be and how could I treat them? 