Has anyone found success in stopping chronic diarrhea in cats?

For context, my cat is 8 years old. For the past 2 years she suddenly began experiencing diarrhea and was seen by the vet many times. Nothing could be found as the cause and so for the past 2 years it's been "try this, try that" over many different vets. From switching foods, diets, meds, probiotics... nothing has helped but Metronidazole. From my understanding this is not meant to be a long term solution, but it is all that is holding my sanity together. Has anyone found success with anything specific that I could bring up at our next visit as a possibly try?

Side note: is chronic diarrhea a common thing? to just start out of nowhere and have what seems to be no logical reason for happening.