What is this dark mark on my incision scar? (photo)

I had a breast aug 9 months ago, and in the early weeks following the op one of my scars showed signs of a little bleeding where it hadn't healed as well as the rest of the incision. I treated this with iodine and kept it covered as recommended by my surgery. It cleared up over time as normal. However, this little brown mark has never gone. It's smooth to touch (I massage the scars with oil twice a day) but up close it does look like a little scab or blood blister. Should I seek advice from a GP?