Why isn't Liverpool cream an option T? I've had some success with thuja cream at 30C potency but tbh, it's possible that the dodgy patches of crusty skin were not true sarcoids. Thuja cream is more effective than the tablets as with the tablets, you're supposed to have ultra clean hands, no strong smells on them, no mints given to the horse etc etc. Thuja cream you just rub in a few times a week.
My old mare used to get these on her inner thigh and the vet would nick the skin with a scalpel and pop them out once they got to the size of a pea/grape, then spray the hole with purple spray.