I had a blue and seal point cross, Twinkle, for 22 years. He was a dear boy and stayed pretty healthy to the end. Siamese are long livers and Oliver sounds like he will be around for a long time. Twinky had some non-cancerous fat deposits on his tummy and below his ear. In those days (1960-1982) we did not have the vet services to remove these or we would have done so just to make him feel more comfortable and look better.
Oliver is a beautiful boy and worth every penny to keep him healthy for years to come. All the best to him and his owner.