I have an arab who gets girth gall. If he has sores, i'm like Jazzy, I swear by white healer, or if I have none, pawpaw ointment. Once it's healed, I ALWAYS keep his girth area clipped, it stopped dirt and sweat building up which was the main culprit. While it was bad, the anti-gall girth didn't help, I had to buy a REAL sheepskin girth cover. Don't go for the synthetic ones, they make it worse! I tried! Once he healed completely, I still keep it clipped and he doesn't need the girth cover any more, and hasn't gotten any gall for a long time.
Hope he is getting better!