I understand you aren't a vet. I appreciate your input nonetheless.
I've only been treating him for mud fever in the time i've had him, which has been under a year. His previous owner advised that he's always had the scabs during the time she owned him (3+ years) so i'd say it's something he's been living with it for a number of years untreated.
I will get a second opinion from a different vet and see if they can advise me further.