I have a 13 years old male Brittany Spaniel. We found a tiny

Hi, my name is Tony. I have a 13 years old male Brittany Spaniel. We found a tiny hole (1/2cm or 1/4 inch) which was weeping on Buster's right back leg inside his knee. We took Buster to the vet and now treating him with antibiotic tablet for 2weeks, but the hole is not closing. We can see shiny metal at the bottom of the shallow hole. In April 2018 Buster's cranial cruciate ligament ruptured. He had Tibial Plateau Levelling Osteotomy (TPLO surgery). Since then he had not have a problem on his leg. He did not develop any surgical site infection at all. But on 7th June 2022 the vet suggested that the metal plate in his leg might be rejected by his body after 4 years. The vet sugested that X-ray for further investigation and surgery to remove metal plate and screws might be needed. We do not want another operation as Buster is nearly 13 years old and unsteady on his feet anyway. He may not be able to walk after the removal of the plate. We want to treat him more conservatively as he is old. Also, pet insurance company will not cover the cost, as it is regarded as an existing condition. What can we do to treat Buster without having an operation of removing the plate? Is it possible to use antibiotics for a long term? So far 2 weeks of Synulox did not make a big difference. For example, I have had a splenectomy and I have to continue with life-long Penicillin V 250mg twice a day to prevent infections. Normally they say you cannot have antibiotics for a long term treatment. What is the option here? Buster is getting old and cannot go for a long walk but otherwise happy and healthy. The wound is not bothering him at all so far. We don't know what to do next.
JA: What sort of animal are we talking about?
Customer: Brittany Spaniel, it is a dog
JA: I'll do all I can to help. What is wrong with the Brittany?
Customer: I have just spent 20 mins typing above and explained everything to you .
JA: Where does the Brittany seem to hurt?
Customer: have you read what I have put down when you asked me your first question ?
JA: Can you see anything that looks wrong or different?
Customer: We are getting nowhere as I have given you every bit of information above in answer to your first question.
JA: Is the Brittany eating normally?
Customer: canyou please put someone else on the line as we are getting nowhere.
JA: Is the Brittany having trouble peeing or pooing?
Customer: are you a robot
JA: Yes, I'm a bot. I make the process of talking to the Vet more efficient and affordable by asking basic questions. How is the Brittany behaving differently?
Customer: All you need to know i have explained after your first question
JA: What is the Brittany's name and age?
Customer: sorry I have to go to another site as i cannot comunicate with you.
JA: Is there anything else the Vet should know before I connect you? Rest assured that they'll be able to help you.
Customer: no please connect me