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Ever consider CBD ?
Be careful with aspirin. Bad reactions are common.
Look for Carprofen. It's not that expensive. Looks like Chewy has it for down around .50-.70 a pill. Other meds like aspirin and acetaminophen can be toxic after long periods of taking it.
My vet prescribed Meloxicam for my old dog. She did bloodwork before and again after thirty days to make sure he was tolerating it. It made a huge improvement in his comfort level and what he is able to do.