I need advice about my horse's sarcoids from experienced horse owners.?

This doesn't make sense. Did your vet say you should use castor oil or are you just taking a recommendation from your friend and you have not told your vet? It sounds like the vet's treatment was working with one lingering area; then you took advice from someone who has no medical background and it is getting worse. You have to follow the advice given by your vet or do it on your own and be prepared to accept the consequences. Seems to me the oil has aggravated the area. You do understand that these cells can change into a more aggressive form? If this is such a tenuous condition and you have grave concern, you should come clean with your vet and follow his recommendations strictly. If you do not, you cannot expect to hold your vet responsible if you have a less than optimum outcome. When you withhold information from your vet, you are making it impossible to do his job well. Bleeding is not good. have you shared this information? You must keep your vet informed if you want him to help you. And you have to make a decision about care. If you are not going to follow the vet's advice, there is no reason to pay him more money. If money is an issue, just make a choice. If you interfere with the prescribed treatment, it could make your financial investment much larger than it would have been. Think about it, but you have to be honest with the vet. Hope your horse improves.