Im glad jr posted as I would say chat with your farrier. My paint had quarter cracks in both front feet when I got him 7 years ago and they stayed there for about 5 years, with attentive shoeing. Never a problem but had to be managed. I found supplements to be a total waste of money. The cracks have completely closed up now for the past few years tho, might come back but as of today they are not. They never caused my horse any problems. I had been told it could be a little piece of sand din there and I should have him sedated and worked on, but i'm glad I didn't and he is fine but I totally trust my farrier and his advice.
I would chat with the farrier first and even consider x-ray's. I got a horse in January that had a front left hoof crack. He has always been sound and can jump the moon but we got x-ray's at a podiatry clinic and come to find out he had broken a small bone in his hoof a long time ago, they said he'll be fine to compete and even might go to **** shows, but it's very nice to know when a horse has something like that. It could also be a bruise on the coronary band which is causing a crack.