You won't receive another answer from an expert unless I'm really off track. Several experts review this posting and unless someone disagrees, they won't "overpost". Some veterinarians shy away from sinus xrays as they aren't always easy to take. I don't worry about anesthetizing older dogs if they have good liver and kidney function. I've NEVER lost one under anesthesia, and the anesthetic is very short acting. Old age is not a disease. I think of invasive procedures as those that enter a body cavity like biopsies and exploratory surgeries. Looking with a scope or an xray is about as non-invasive as you can get. I'm sure he was concerned about anesthesia, but if the right drugs and monitoring are used, it should be safe.
I would ask your vet about sinus xrays. Seems logical to me.
Good luck and let me know if you need further information.
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