Well, it depends on what the problem is, but if it’s an infection or sludge he will need some meds or instructions on care. I think it’s a good time to meet the vet. I don’t want to be wrong in my advice, but sometimes a discomfort can be temporary. This would potentially be more serious in a bunny his age so I would like you to be sure. A geriatric bunny needs a good relationship with a vet since you may find you are seeing one more frequently from now on.
My Spockie lived to be 8, and he was disabled in his back legs for many months, but he coped surprisingly well and had a good disposition and a will to live so we made some adjustments.
Here’s a link to an excellent website that has information on older and disabled bunnies. http://www.catsandrabbitsandmore.com/disabled_rabbits
I was bathing him more frequently, found some washable beds that were soft and comfy when he became incontinent, etc. You may not be at that point for many years to come, but it’s a good time to become familiar with what to do to make your lives as pleasant and comfy as possible.
Hope he likes the new vet. 